As they ministered to the Lord, and fasted, the Holy Ghost said, Separate me Barnabas and Saul for the work whereunto I have called them (Acts 13:2)

God had planned for Paul to go on missionary journeys all along, and Paul knew it. I believe the reason Paul and Barnabas even came together was because they sensed something was going on in their spirits and decided to pray it through.

Although Paul knew what God called had him to do, Paul did not step out and do it until God said to do it. He did become an apostle or a preacher until God told him to be one.

This helps us to look at the other side of this issue of staying in God's timing. Just because you are pregnant, doesn't mean you are going to give birth tomorrow. When you sense that God is calling you to do something, wait on God. Discern His timing. Make sure you are stepping out when God says to step out.