The possible interruption of conjugal rights, for the sake of prayer, is only a concession, not a command.
Paul perhaps makes this concession in recognition of the Jewish background of some church members (see notes under 1 Corinthians 7:5; Acts 18:1–11).
Some interpreters (notably in the Roman Catholic tradition) have argued that Paul refers to marriage itself, when he speaks of a concession.
The implication is that marriage, while permissible, is a less than ideal state for a Christian. Yet this view of marriage is unbiblical and unattested to in Paul’s other writings (see, e.g., Ephesians 5:22–33).
6 Now as a concession, not a command, I say this.