Romans 15:28

When therefore I have performed this, and have sealed to them this fruit, I will come by you into Spain.

Paul intended first to finish carrying the offering of the Gentile believers to the poor at Jerusalem, and only after that task was performed to travel onward by way of Rome to Spain. The fruit he spoke of sealing to them was that material contribution, given as the tangible expression of the Gentiles sharing in spiritual blessings. He gathered it in part to open the way for preaching in Jerusalem among those who did not believe that Jesus had risen and is the living Son of God.

That projected journey by way of Rome into Spain was service for God. Fitness for such service comes only when mental power and the talent of speech are sanctified.