Actually, the purpose of a Christian marriage is the avoidance of sin.
Paul makes it quite clear in 1 Corinthians 7:1 Now concerning the things of which you wrote to me:
It is good for a man not to touch a woman. 2 Nevertheless, because of sexual immorality, let each man have his own wife, and let each woman have her own husband. 3 Let the husband render to his wife the affection due her, and likewise also the wife to her husband. 4 The wife does not have authority over her own body, but the husband does. And likewise the husband does not have authority over his own body, but the wife does. 5 Do not deprive one another except with consent for a time, that you may give yourselves to fasting and prayer; and come together again so that Satan does not tempt you because of your lack of self-control. 6 But I say this as a concession, not as a commandment. 7 For I wish that all men were even as I myself. But each one has his own gift from God, one in this manner and another in that.
8 But I say to the unmarried and to the widows: It is good for them if they remain even as I am; 9 but if they cannot exercise self-control, let them marry. For it is better to marry than to burn with passion.
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children, of course, are a loving byproduct of the marriage.We are to, of course, be fruitful and multiply.
Homosexuality is a sin and an unnatural union. Heterosexual marriage is not just for a sense of procreation but more than that it is for us to not burn with passion and to be able to walk righteously in God's way by not giving ourselves over to sexual immorality.
I hope that helped answer your question.
