The commitment in the Christian life is to follow Christ. We do that by the truth of His Word, the leading of His Holy Spirit and a focus on Him whether our circumstances are easy or fraught with difficulty. Perhaps the most important aspect of commitment is belief. When we deeply believe something it’s a far simpler thing to make, and keep, a commitment.
“Looking back” in the above verse suggests someone who makes a commitment to a certain course, in this case the commitment to follow Christ, then thinks back to a time when life required less and considers quitting the present course of action. One thing we know we can expect from commitment is that it's going to require something of us. That something might be work or faith or trust or an absolute determination not to give up. Whatever it requires, it will make demands on us and when they become onerous our temptation is to look back to a time when we think we had freedom.
Abraham was one who made such a commitment of faith that he shines as an example in scripture. As a man without a child he was given a promise by God when he was a very old man that he would be the father of many. Because the promise was given by God it would have been easy to believe initially. However, the years rolled by and still there were no children yet Abraham believed and kept his commitment to trust God to fulfill His promise.
It would have been understandable for Abraham to be discouraged and give up his expectation but this verse tells us instead his faith grew stronger. He’d made a commitment to believe the promise God had given, he stuck to that commitment of faith and saw the fulfillment of the promise. Not only did he have a son but God Himself declared Abraham a righteous man. And that's as good as it gets!
God has given every single one of us promises we can trust. His commitment is to fulfill those promises. Our commitment is to trust and obey. Looking back is a way of seeking answers or fulfillment in the systems of this world which eventually disappoint us or lead us away from our commitment to Christ. It is our duty, and indeed our very great joy, to keep our hands on the plough with our eyes on Christ and we will reap the blessings of a life wholly committed to Him.