This passage of Scripture tells us that His divine grace manifests itself and covers us more abundantly during our trials. His strength compliments our inherent weakness. His sufficiency fulfills what is lacking in us. The power of Christ sustains us during our trials.
In the surrounding context of 2 Corinthians 12:9, the Apostle Paul was telling the Church of Corinth how God did not accept his petition to remove his distress, but rather assisted him when he was grieving about Satan irritating him after he had received personal revelation that he was not allowed to communicate to other men (v. 7).
Thus, we see that the Lord permits us to undergo temptations for the sake of building us up. We can build up our spiritual strength for times of infirmity through the persistent resistance of temptation and continued obedience to God.
We need to trust in God and His sufficient grace. We, in the same manner as the inspired writer Paul, can confidently proclaim Jesus Christ as Lord because He is faithful and trustworthy. He is with us, even during times of hardship (v. 10).