Everything the Church teaches about Marriage and the purpose of the conjugal act can be linked back to “man” (both male and female) as being God’s creation in His image and likeness, and to the means of the generation of human life:
"God is love and in himself he lives a mystery of personal loving communion. Creating the human race in his own image… God inscribed in the humanity of man and woman the vocation, and thus the capacity and responsibility, of love and communion" (FC 11).
"God created man in his own image . . . male and female he created them" (Gen 1:27); He blessed them and said, "Be fruitful and multiply"(Gen 1:28); "When God created man, he made him in the likeness of God. Male and female he created them, and he blessed them and named them Man when they were created" (Gen 5:1-2). (Catechism of the Catholic Church, 2331, emphasis mine)
Sexuality affects all aspects of the human person in the unity of his body and soul. It especially concerns affectivity, the capacity to love and to procreate, and in a more general way the aptitude for forming bonds of communion with others (CCC 2332, emphasis mine).
Each of the two sexes is an image of the power and tenderness of God, with equal dignity though in a different way. The union of man and woman in marriage is a way of imitating in the flesh the Creator's generosity and fecundity: "Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh" (Gen 2:24). All human generations proceed from this union (cf. Gen 4:1-2, 25-26; 5:1). (CCC 2335, emphasis mine)
As the debate over the definition of Marriage (and whether same-sex-attracted persons have a “right to Marriage”) continues, it would be helpful to understand what the Church teaches about Marriage and what it understands in regards to homosexuality. A Catholic, or ANY Christian for that matter, can be quickly mislabeled as a bigot for not supporting a same-sex union, or for not supporting a re-definition of Marriage. To understand how the Christian position is not bigoted, it is helpful to know what that position is.
First and foremost, it must be noted that the Church is not “against” people with same-sex-attractions. The Church is “for” ALL people, regardless of our inclinations. The Church recognizes the suffering of people with these same-sex-attractions and calls all the Christian faithful to love our neighbors as we help each other find a more intimate relationship with Christ.
Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained ( CCC 2357).
The number of men and women who have deep-seated homosexual tendencies is not negligible. This inclination, which is objectively disordered, constitutes for most of them a trial. They must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God's will in their lives and, if they are Christians, to unite to the sacrifice of the Lord's Cross the difficulties they may encounter from their condition (CCC 2358, emphasis mine).
At the same time, the Church recognizes that God desires the salvation of ALL His children, and that we are called to live according to His commands. In choosing to disobey God, we reject His Authority over our lives, and reject Him as our Lord. There are a multitude of examples in Scriptures where Christians are called to guide one another from sin toward God . Obeying God’s Word, the Church admonishes us:
Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity (cf. Gen 191-29; Rom 124-27; 1 Cor 6:10; 1 Tim 1:10), tradition has always declared that "homosexual acts are intrinsically disordered" (CDF, Persona humana 8). They are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved (CCC 2357, emphasis mine).
Instead of suffering sin upon our neighbor (Lv 19:17), we call him to the same vocation that EVERY Christian is called to: chastity.
Homosexual persons are called to chastity. By the virtues of self-mastery that teach them inner freedom, at times by the support of disinterested friendship, by prayer and sacramental grace, they can and should gradually and resolutely approach Christian perfection (CCC 2359, emphasis mine).
All the baptized are called to chastity. The Christian has "put on Christ" (Gal 3:27), the model for all chastity. All Christ's faithful are called to lead a chaste life in keeping with their particular states of life. At the moment of his Baptism, the Christian is pledged to lead his affective life in chastity (CCC 2348, emphasis mine).
"People should cultivate [chastity] in the way that is suited to their state of life…whether they are married or single" (CDF, Persona humana 11). Married people are called to live conjugal chastity; others practice chastity in continence:
“There are three forms of the virtue of chastity: the first is that of spouses, the second that of widows, and the third that of virgins. We do not praise any one of them to the exclusion of the others. . . . This is what makes for the richness of the discipline of the Church” (St. Ambrose, De viduis 4,23:PL 16,255A) (CCC 2349, emphasis mine).
The Church does not forbid Marriage, as the Church understands Marriage, for any person unless there is some impediment to Marriage (such as permanent, antecedent, and incurable impotence…not to be confused with infertility, or if one party is already Married, etc.). Every human person who is properly disposed to Marriage has the freedom to enter into Marriage, which is a lifelong, monogamous relationship with a person of the opposite sex.
What we do NOT have the freedom to do is redefine what Marriage *is* and expect God to change His own covenant sign. We do not have a right to engage in carnal activities and simultaneously expect God to recognize each and every carnal act as a “Marital” act. God created Marriage for a very specific purpose, with very specific ends and components.
Marriage is a life-long union, a commitment, between a man and a woman, which is ordered toward the generation and education of children. If a union between two persons is neither life-long (the two do not actually have a true commitment between them) nor ordered toward generation (meaning they don’t have the complementary sexual organs that could at least potentially generate life, even considering old age or natural loss of functionality), there is no true Marriage.
To understand more about this, we need to understand sexuality and conjugal love, and how these fit into Marriage.
Sexuality is ordered to the conjugal love of man and woman. In marriage the physical intimacy of the spouses becomes a sign and pledge of spiritual communion. Marriage bonds between baptized persons are sanctified by the sacrament (CCC 2360, emphasis mine).
The spouses' union achieves the twofold end of marriage: the good of the spouses themselves and the transmission of life. These two meanings or values of marriage cannot be separated without altering the couple's spiritual life and compromising the goods of marriage and the future of the family (CCC 2363, emphasis mine).
Fecundity is a gift, an end of marriage, for conjugal love naturally tends to be fruitful. A child does not come from outside as something added on to the mutual love of the spouses, but springs from the very heart of that mutual giving, as its fruit and fulfillment. So the Church, which is "on the side of life" (FC 30), teaches that "it is necessary that each and every marriage act remain ordered per se to the procreation of human life" (HV 11). "This particular doctrine, expounded on numerous occasions by the Magisterium, is based on the inseparable connection, established by God, which man on his own initiative may not break, between the unitive significance and the procreative significance which are both inherent to the marriage act" (HV 12; cf. Pius XI, encyclical, Casti connubii). (CCC 2366, emphasis mine)
Called to give life, spouses share in the creative power and fatherhood of God (cf. Eph 3:14; Mt 23:9). "Married couples should regard it as their proper mission to transmit human life and to educate their children; they should realize that they are thereby cooperating with the love of God the Creator and are, in a certain sense, its interpreters. They will fulfill this duty with a sense of human and Christian responsibility" (GS 50 § 2). (CCC 2367, emphasis mine)
This brings us back to Marriage.
"The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament" (CIC, can. 1055 § 1; cf. GS 48 § 1). (CCC 1601, emphasis mine)
Sacred Scripture begins with the creation of man and woman in the image and likeness of God and concludes with a vision of "the wedding-feast of the Lamb" (Rev 19:7, 9; cf. Gen 1:26-27). Scripture speaks throughout of marriage and its "mystery," its institution and the meaning God has given it, its origin and its end, its various realizations throughout the history of salvation, the difficulties arising from sin and its renewal "in the Lord" in the New Covenant of Christ and the Church (1 Cor 7:39; cf. Eph 5:31-32). (CCC 1602, emphasis mine)
"The intimate community of life and love which constitutes the married state has been established by the Creator and endowed by him with its own proper laws. . . . God himself is the author of marriage" (GS 48 § 1). The vocation to marriage is written in the very nature of man and woman as they came from the hand of the Creator. Marriage is not a purely human institution despite the many variations it may have undergone through the centuries... "The well-being of the individual person and of both human and Christian society is closely bound up with the healthy state of conjugal and family life" (GS 47 § 1). (CCC 1603)
For man is created in the image and likeness of God who is himself love (cf. Gen 1:27; 1 Jn 4:8, 16). Since God created him man and woman, their mutual love becomes an image of the absolute and unfailing love with which God loves man. It is good, very good, in the Creator's eyes. And this love which God blesses is intended to be fruitful… "And God blessed them, and God said to them: 'Be fruitful and multiply, and fill the earth and subdue it'" (Gen 1:28; cf. 1:31). (CCC 1604, emphasis mine)
Holy Scripture affirms that man and woman were created for one another: "It is not good that the man should be alone" (Gen 2:18). The woman, "flesh of his flesh," his equal, his nearest in all things, is given to him by God as a "helpmate"; she thus represents God from whom comes our help (cf. Gen 2:18-25). "Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh" (Gen 2:24). The Lord himself shows that this signifies an unbreakable union of their two lives by recalling what the plan of the Creator had been "in the beginning": "So they are no longer two, but one flesh" (Mt 19:6). (CCC 1605, emphasis mine)
The entire Christian life bears the mark of the spousal love of Christ and the Church. Already Baptism, the entry into the People of God, is a nuptial mystery; it is so to speak the nuptial bath (cf. Eph 5:26-27) which precedes the wedding feast, the Eucharist. Christian marriage in its turn becomes an efficacious sign, the sacrament of the covenant of Christ and the Church. Since it signifies and communicates grace, marriage between baptized persons is a true sacrament of the New Covenant (cf. DS 1800; CIC, Can. 1055 § 2). (CCC 1617, emphasis mine)
So there you have it. This is a decent glimpse into the Church's pro-person, pro-Marriage, pro-God teachings on homosexuality and Marriage, which are based on the Truth inscribed in the humanity of man and woman. For a more in-depth look, please click on the link (in my "Links" column) titled "Catechism of the Catholic Church, Keyword Searchable" and simply type in whatever word or phrase you want to explore.
 Mt 7:5, Mt 18:15-17, 1 Cor 5:1-13, Gal 6:1-2, James 5:19, Lev 19:17, 2 Thess 3:14, Col 3:16, 1 Thess 5:14, etc… Correcting the Sinner is Not Being Judgmental