Paul was writing to people who, in becoming Christians, had made a massive break with their prior life -- just like he had.  True, he left Judaism and they left paganism, so the contexts differed.  But  they were united in the same faith and shared a common course: 

​

           Not that I have already obtained all this, or have already been made perfect, but I press on to take hold of that for which Christ Jesus took hold of me.  Brothers, I do not consider myself yet to have taken hold of it. But one thing I do: Forgetting what is behind and straining toward what is ahead,  I press on toward the goal to win the prize for which God has called me heavenward in Christ Jesus (Phi 3:12-14).

          

The fundamental change in his life occurred when "Christ Jesus took hold of me."  In response, he had taken hold of that new life, though it was not yet perfected.  "Forgetting what is behind" -- for him, the fake holiness of legal obedience; for the Gentiles, the false religions of Greece and Rome; "straining toward what is ahead" -- our citizenship in heaven (Phi 3:20) ("our commonwealth" RSV).  Paul uses a unique word in the New Testament (politeuma), which refers to political membership.  Once separated by vastly different and opposing social backgrounds, Paul and his readers now shared a trans-national, supernatural citizenship that would endure into eternity.