Paul was describing his experience when he was trying to live the Christian life. Romans 8 is the answer. Paul also said this:
2 Corinthians 6:
4Rather, as servants of God we commend ourselves in every way: in great endurance; in troubles, hardships, and calamities;
5in beatings, imprisonments, and riots; in labor, sleepless nights, and hunger;
6in purity, knowledge, patience, and kindness; in the Holy Spirit and in sincere love;
7in truthful speech and in the power of God; with the weapons of righteousness in the right hand and in the left;
8through glory and dishonor, slander and praise; viewed as imposters, yet genuine;
9as unknown, yet well-known; dying, and yet we live on; punished, yet not killed;
10sorrowful, yet always rejoicing; poor, yet making many rich; having nothing, and yet possessing everything.
11We have spoken freely to you, Corinthians. Our hearts are open wide.
12It is not our affection, but yours, that is restrained.
13As a fair exchange, I ask you as my children: Open wide your hearts also.
It does not sound like a struggling, defeated sinner to me. Either Paul had come into victory or he was lying his head off.