This is a faithful saying - See the notes at 1 Timothy 1:15. The reference here is to what he had been just saying, meaning that the doctrine which he had stated about the method of salvation was in the highest degree important, and entirely worthy of belief.
And these things I will that thou affirm constantly - Make them the constant subject of your preaching. “That they which have believed in God might be careful to maintain good works.” This shows that Paul supposed that the doctrines of the gospel were fitted to lead people to holy living; compare Titus 3:1, and the notes at Philippians 4:8. The “good works” here refer not merely to acts of benevolence and charity, but to all that is upright and good - to an honest and holy life.
These things are good and profitable unto men - That is, these doctrines which he had stated were not mere matters of speculation, but they were fitted to promote human happiness, and they should be constantly taught.