Mission to Gentile

Romans 15:14-3
God gave Paul the priestly duty of proclaiming the gospel of God, so that the Gentiles might become an offering acceptable to God, sanctified by the Holy Spirit.
“Those who were not told about him will see, and those who have not heard will understand.”  This is why I have often been hindered from coming to you. 
So Paul did what can do to preach Gospel in that area.
Therefore I glory in Christ Jesus in my service to God.
After he delivered the gifts from Macedonia area, Paul hopes visit Spain while passing through and  have enjoyed your company for a while.
In closing, Paul speak personally.  For more than 20 years he has been an apostle to the non-Jewish world.
He has seen churches established all over Cyprus, Syria, Turkey and Greece.
Now he has completed his work and discharged his responsibilities.
Once the business of delivering the money given by Gentile churches to Jerusalem is over,  he can look west to Spain., calling at Roman on the way.
Why?