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 word form here in the NKJV is the word pattern in the NET and it seems to bring a little more clarity to the verse. The picture presented is of making something that looks like or conforms to an original. Here the Roman believers were allowing themselves to be molded and shaped to the teachings of the gospel through the daily process of sanctification.
Picture molten metal being poured into a mold and the molten metal taking the shape of the mold. The believer is the molten metal, and the mold is the doctrine and teaching of the gospel. Molten metal does not retain any of the form that it had before being melted down. As we walk with the Lord, He will work to melt down any remaining fragments from our old life in order that we become more Christ like. This refining process is not easy, but it is necessary so that God can use us to the fullest as we serve Him here on earth. Let us yield to God’s work on our lives, leaving behind the old man and putting on the new man (Ephesians 4:22 – 24)
Pastor Jeff Mericle