Jamieson, Fausset and Brown on 1 Corinthians 7:25

25. no commandment of the Lord: yet ... my judgment--I have no express revelation from the Lord commanding it, but I give my judgment (opinion); namely, under the ordinary inspiration which accompanied the apostles in all their canonical writings (compare 1Co 7:40; 1Co 14:37; 1Th 4:15). The Lord inspires me in this case to give you only a recommendation, which you are free to adopt or reject--not a positive command. In the second case (1Co 7:10, 11) it was a positive command; for the Lord had already made known His will (Mal 2:14, 15; Mt 5:31, 32). In the third case (1Co 7:12), the Old Testament commandment of God to put away strange wives (Ezr 10:3), Paul by the Spirit revokes.

mercy of the Lord--(1Ti 1:13). He attributes his apostleship and the gifts accompanying it (including inspiration) to God's grace alone.

faithful--in dispensing to you the inspired directions received by me from the Lord.