‘But thanks be to God, that, whereas you were servants of sin, you became obedient from the heart to that form of teaching to which you were delivered, and being made free from sin, you became servants of righteousness.'
But Paul now thanks God that while his hearers had been the servants of sin, they had responded from their hearts to the ‘form of teaching' that they had received. There is possibly an indication here that even by this stage there was a ‘form of teaching' delivered to new Christians, possibly prior to or immediately following baptism. Or it may have reference to the body of tradition about Jesus Christ that had been put together by the Apostles (possibly called ‘The Testimony of Jesus' compare Revelation 1:2; Revelation 1:9; Revelation 12:17; Revelation 19:10; and see 2 Timothy 1:8). And they had become ‘obedient from the heart' to it. Thus they had been freed from sin's servitude, and had become servants of righteousness. Experiencing the righteousness of God when they had been ‘accounted as righteous', they had then become servants of righteousness, living it out in their lives.
Paul clearly considered that it was important that they recognised what obedience to God meant. It did not mean following their own inclinations and ideas about God. Rather it meant responsive obedience to His revealed truth. Today that ‘form of teaching' is found substantially in the New Testament. We do well to ensure that we live according to it.