I Corinthians 16:9 For a great door and effectual is opened unto me, and there are many adversaries.
God has opened a great, effectual, door of ministry for Paul. He is excited about the opportunities that God has given him. However, he does know that with opportunity comes obstacles. He knows that with every advantage the Lord gives us we will find adversaries.
So as you launch forth in your service and ministry to the Lord watch for those open doors. Watch for Him to do great things and give you opportunities that you could never have hoped for but at the same time know that there will be trouble.
Some get discouraged because there are problems. Problems are what we should expect. Always be watching and praying. Always be going through doors but do not let problems discourage but rather encourage. There are so many problems or obstacles because the prospect or opportunity to do something for God is so great.