Don’t turn back. Paul is reminding the people what they left and telling them to be sure to not turn back. Read Galatians 4:8-11.
However at that time, when you did not know God, you were slaves to those which by nature are no gods. But now that you have come to know God, or rather to be known by God, how is it that you turn back again to the weak and worthless elemental things, to which you desire to be enslaved all over again? You observe days and months and seasons and years. I fear for you, that perhaps I have labored over you in vain.
Galatians 4:8-11 NASB
We have been adopted as sons and daughters. We are heirs of God. Why would we ever want to consider turning back to our prior ways? Yet that is very often exactly what we do. God is God. He is worthy of our praise and once we know what He has for us, then we will never want anything else. Stay focused in Him and don’t turn back.