There is a difference between doubting and “looking back” in the sense that Jesus uses the term in Luke 9:62. I personally know many believers who have doubts and struggles of various kinds and nevertheless keep on plowing forward for the Lord. To “look back” means to desire to give up your Christian life altogether. It means taking your hand off the plow and walking away from the field, so to speak. A man may have many thoughts or worries or concerns and yet keep his hand on the plow. God bless that man who plows on for Jesus despite his doubts.

Those who truly turn away perhaps never really believed in the first place. Jesus means to say that serving him demands our full commitment.

See my podcast on If I Believe, Why Do I Doubt?