Hi, I'll get the ball rolling with a few basic ones.
- Apostle to the Gentiles. Basically means he was able to speak about Christianity effectively to non-Jews. Places in Eastern Europe, Greece and eventually Rome would convert based off of his understandings. Larger population and with Rome's uptake of Christianity the religion was exposed to the entire empire.
- Input to the New Testament. 13 of the 27 books in the New Testament were written by Paul, huge input in to the development of Christianity. This incorporates now broadly accepted messages of the Christian faith.
- Distinguished Christianity from Judaism. After being a Pharisee, he worked hard to differentiate Judaism from Christianity to avoid its continued persecution.
- Consolidated the Church. Using the teachings of Jesus, explained them in depth from a Pharisee's perspective and then applied them to new situations in the church.
Hopefully that helps, good luck!