Romans 6:17

Thanks be to God, &c. He thanks God, not because they had been in sin, but because after having been so long under the slavery of sin, they had now been converted from their heart, and with their whole strength gave themselves to that form of doctrine to which they had been conducted by the gospel. He returns God thanks for their obedience to the faith, because this obedience of the human will is the work and gift of God, that so no one may glory in his sight. (Ephesians ii.) (Estius)