Paul constantly considered himself the least of the disciples. Much like John the Baptist, he considered himself the least worthy of grace, however, the bible teaches us that the exalted will be made low and the humble will be exalted. The difference is that God recognized Paul's (then Saul's) zeal and saw him to be a great servant in spreading the word and being a testimony to God's power.
The system that exists now is a man-determined process, whereas at that time, it was a God-determined process.