Albert Barnes on Romans 15:23

But now, etc. Having no further opportunity in these regions to preach to those who have never heard the gospel.

In these parts. In the regions before specified, he had gone over them, had established churches, had left them in the care of elders, (Acts 20:17) and was now prepared to penetrate into some new region, and lay the foundation of other churches.

And having a great desire, etc. See Rom 1:9-13.