To deprive someone is to withhold from him what rightfully belongs to him. Another valid translation would be, Do not rob each other.
With this command, Paul emphasizes that sexual intimacy is a duty within marriage.
Paul leaves room for one exception. Both spouses may agree to abstain from sex for a limited time,
and only for the sake of devotion to prayer. This seems to resemble the act of fasting, where one’s own pleasures and comforts are given up for a time for the sake of earnest prayer.
In the Old Testament, sexual abstinence was associated with ritual purity (see, e.g., Exodus 19:14–15; Leviticus 15:18; 1 Samuel 21:4). The practice of abstaining from sex for a time, for the sake of prayer, was also known among the Jews of Paul’s time.
Among the Jews, the husband would be the one to take the oath, although his wife usually had to agree to it first. Pharisaic schools also stipulated the maximum period of time for which such an oath was valid. One school stipulated one week, another, two weeks.
The reason why sexual abstinence should not be prolonged is because it will create room for Satan’s temptations (see further 1 Corinthians 7:2).
5 Do not deprive one another, except perhaps by agreement for a limited time, that you may devote yourselves to prayer; but then come together again, so that Satan may not tempt you because of your lack of self-control.