The Mystery of the Gospel Revealed (v.1-13)
Paul was made to understand through revelation that gentiles are eligible to take part in the gospel through Jesus. God gave him the job of preaching to the gentiles, he is the least of the saints.
So basically Paul is saying that he is bringing the gentiles into the fold. He is basically saying to the people he is talking to that they are also eligible for heaven. I think he was trying to be humble when he said he was the least of the saints, but it was right next to a line about how he is in charge of bringing gentiles to Christ, so it almost reads like it is a dig at them. I don't think that is the intention or anything, but it did make me laugh.
Prayer for Spiritual Strength (v.14-21)
This basically just says that everyone should pray for strength.