This is a very realistic approach to sex and marriage. Realism demands that we acknowledge the very powerful desire created in man and woman by God, a lesson the child of God forgets to his harm. The Bible teaches this in two ways. This itself overthrows the teaching that sex in marriage is only for producing children. Paul ,means that it is better to marry than burn in one's lusts.
Marriage is the remedy for that.
Christian husbands and Christian wives owe it to their spouse to give themselves to each other physically. And because this is Jesus' command, you owe it to Jesus to give yourself to your spouse. The reason this is a debt Paul gives in the next verse. If Christian couples do not live in this way, Satan will tempt them for their abstinence. This is the teaching of I Corinthians 7 in verse 5.