When I was a boy on the farm, my dad would tell me, "You can't plow a straight row if you look back." You can test this for yourself by looking back as you walk through snow or along a sandy beach. Your tracks won't be straight.
A good farmer doesn't look back once he has put his hand to the plow. Jesus used this analogy to teach us that if we are to be His disciples we must make a complete break with all loyalties that hinder our relationship with Him.
Total allegiance to God is a principle that is rooted in the Old Testament. The Israelites, after being freed from slavery and fed by supernatural means, looked back longingly to the days when they enjoyed fish, cucumbers, melons, leeks, onions, and garlic in Egypt (Numbers 11:5-6). God was greatly displeased, and He judged His people. Their looking back indicated a lack of commitment to Him.
Today, people who cling to old sins and the worldly pleasures they enjoyed before becoming Christians cannot be loyal disciples of Jesus Christ. When we repent and believe in Him, we become citizens of a new kingdom. We are to break with the sins of the past.
Discipleship means no looking back. — Herbert Vander Lugt
As a follower of Jesus,
I am walking in His way;
Straight ahead till life is over,
I will walk with Him each day. —Hess
In the dictionary of discipleship, you won't find the word "retreat."