Paul was a Jew, a Pharisee of the Pharisees. Paul knew the law probably as good as anyone at the time, practiced the law as well as if not better than anyone at the time, had a personal encounter with Jesus Himself, received more Grace than maybe anyone else at the time because he had persecuted the church yet was saved by and called by Jesus, wrote half the new testament, was filled with the Holy Spirit, saw God do many many things in and through his life..., yet what was Paul's Testimony? He had the information, he knew the Law, he had lived by the Law, the perfect Law of God, but then Jesus ran into Him, and Paul let down his guard for Jesus and submitted his will to Jesus on the road to Damascus on that day when Saul of Tarsus was freed from his own sowing and reaping, and began to enter into Jesus sowing and reaping that Jesus had finished on the cross leaving nothing left to be done. So Paul had the information, and had the Grace, including that he knew as well as anyone the Spirit of the Law..., yet Paul's Testimony was Simply This, that he still couldn't do it, and that many times what he wanted to do that he knew was right, he didn't do, and that which he knew was wrong that he didn't want to do, he still ended up doing..., So he said in no uncertain terms..., “i still can't“ and so..., “oh wretched man that i am! Who will deliver me from this body of death?" "I thank God - through Jesus Christ our Lord! So then, with the mind i myself serve the law of God, but with the flesh the law of sin." Yet still there is now no condemnation to those who are in Christ Jesus, who do not walk according to the flesh, but according to The Spirit. For the law of The Spirit of Life in Christ Jesus has made me free from the law of sin and death.
And we could go on for hours and cover the whole of the bible and get the same answer, that it's all about Jesus and it's not about us to be able to accomplish anything good in and of ourselves. Paul also said in many ways many times that the onus was on God, not on Paul. For instance Paul would say, "He (Jesus) is able to keep that which i have committed to Him against that day." "For i am persuaded that neither death nor life..., nor any other created thing (including himself) will be able to separate him or us (who belong to Jesus) will be able to separate us from the Love of God in Christ Jesus. Far too many Christians are spending too much time staring at their naval thinking that they will soon be able to discover something useful in there..., instead of letting Jesus teach them to stare only at Him and let Him take care of the Rest. This is not a switch that we can flip but rather a process of further dependency on The Person of Jesus.
So in summary, Paul's Testimony was still "i can't but Jesus in me can, and so it was Jesus and Him Crucified, and "i ran better than the rest, yet not i, it was the Grace of God that was in me." So by Grace (that comes from God) we are saved through faith (that comes from God and we use it to connect with Him by faith through Jesus The Door). So then by Grace we are saved, it is the Gift of God to Salvation, and so Grace is the door to Jesus by Faith, and Jesus IS The Door, The Only Door to The Father, by the drawing, wooing, and sealing of The Holy Spirit, and Grace also runs the race. So by Grace we are saved, Grace gets us all the way across the finish line, and Grace also runs the race. If this were not true then Paul's Testimony would be false, and we know it is true, and he would certainly know best aside from Jesus Himself.