That FORM of doctrine..

Do you not know that to whom you present yourselves slaves to obey, you are that one’s slaves whom you obey, whether of sin leading to death, or of obedience leading to righteousness? But God be thanked that though you were slaves of sin, yet you obeyed from the heart that form of doctrine to which you were delivered.
The phrase that form of doctrine is part of a beautiful picture. The word form describes a mold used to shape molten metal. The idea is that God wants to shape us - first He melts us by the work of the Holy Spirit and the Word of God. Then He pours us into His mold of truth - that form of doctrine and shapes us into His image. Adam Clarke on that form of doctrine: “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 believe the Gospel and receiving the Holy Ghost. The words . . . 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.” -David Guzik of www.enduringword.com Romans 6 commentary.

God's Word is awesome, there is so much hidden in there to be searched out. What a blessing it brings when you take the time to search it out.