Adam Clarke on Philippians 3:13

I count not myself to have apprehended - Whatever gifts, graces, or honors I may have received from Jesus Christ, I consider every thing as incomplete till I have finished my course, got this crown, and have my body raised and fashioned after his glorious body.

This one thing I do - This is the concern, as it is the sole business, of my life.

Forgetting those things which are behind - My conduct is not regulated nor influenced by that of others; I consider my calling, my Master, my work, and my end. If others think they have time to loiter or trifle, I have none: time is flying; eternity is at hand; and my all is at stake.

Reaching forth - The Greek word επεκτεινομενος points out the strong exertions made in the race; every muscle and nerve is exerted, and he puts forth every particle of his strength in running. He was running for life, and running for his life.