But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you. But God be thanked, that ye were the servants of sin - This verse should be read thus: But thanks be to God that, although ye were the servants of sin, nevertheless ye have obeyed from the heart that form of doctrine that was delivered unto you; or, that mould of teaching into which ye were cast. The apostle does not thank God that they were sinners; but that, although they were such, they had now received and obeyed the Gospel. The Hebrew phrase, Isaiah 12:1, is exactly the same as that of the apostle here: In that day thou shalt say, I will praise thee, for thou wast angry with me: that is, although thou wast angry with me, thou hast turned away thy wrath, etc.
That form of doctrine - Τυπον διδαχης; here Christianity is represented under the notion of a mould, or die, into which they were cast, and from which they took the impression of its excellence. The figure upon this die is the image of God, righteousness and true holiness, which was stamped on their souls in believing the Gospel and receiving the Holy Ghost. The words εις ὁν παρεδοθητε τυπον refer to the melting of metal; which, when it is liquefied, is cast into the mould, that it may receive the impression that is sunk or cut in the mould; and therefore the words may be literally translated, into which mould of doctrine ye have been cast. They were melted down under the preaching of the word, and then were capable of receiving the stamp of its purity.