Romans 1:9-10

God, whom I serve with my whole heart in preaching the gospel of his Son, is my witness how constantly I remember you in my prayers at all times; and I pray that now at last by God's will the way may be opened for me to come to you.

(v9-10, NIV)

Paul is calling God to witness. He is appealing to his readers and calling God as his witness as he tells them about his prayers for them. He has been and continues to pray for them and have them in his prayers. The problem is that he can't really prove it to them. You can't prove it to others that you've been praying for them or not. This is why Paul calls God to witness to the fact that he's been praying for them. Paul isn't trying to show off or anything, but continue to show them his genuine heart for the believers at Rome.

It's quite possible that some sowed seeds of doubt in their hearts, having them believe that Paul really didn't care about them. They may have deceived the believers at Rome into believing that if Paul really did care for them, he'd have come to them already. However, Paul is trying to convey to them his desire for them by his prayers for them.

Paul is also praying that God would allow him to go to them. He is asking the Lord for an opportunity to be opened for him to go and be with the believers at Rome. Paul understands that whether he goes or not is entirely up to God. Therefore, he is appealing to God to allow him to go. In this, we see that Paul is submissive to the will of God. He is asking but still in obedience to God.