Romans 1:13

I do not want you to be unaware, brothers, that I planned many times to come to you (but have been prevented from doing so until now) in order that I might have a harvest among you, just as I have had among the other Gentiles.

(v13, NIV)

Again, Paul is pressing his point that he wants to be with them. He is clear that he doesn't want them to be ignorant of this fact. He wants them to know that he even planned many times to come to them. Unfortunately, each of his attempts has failed since he was prevented to come to them. Paul is completely submitted to God. He wants to go to see them, but is ultimately under the will of God.

Why does Paul want to come to them? His goal is a harvest among the believers at Rome. He has had harvests among the other Gentiles, but wishes a harvest among them. What is this harvest? Looking back at verse 5, Paul wishes to bring about the obedience that comes from faith. This also includes a mutual encouragement by each other's faith as mentioned in the last verse. The obedience of faith that is brought about is that which the believers are mutually encouraged by though each other's faith. They are one in the same and this is the harvest which Paul is interested in.