They were forbidden of the Holy Ghost to preach the Word in Asia (Acts 16:6).

It is interesting to study the methods of His guidance as it was extended towards these early heralds of the Cross. It consisted largely in prohibitions, when they attempted to take another course than the right. When they would turn to the left, to Asia, He stayed them. When they sought to turn to the right, to Bithynia, again He stayed them. In after years Paul would do some of the greatest work of his life in that very region; but just now the door was closed against him by the Holy Spirit. The time was not yet ripe for the attack on these apparently impregnable bastions of the kingdom of Satan. Apollos must come there for pioneer work. Paul and Barnabas are needed yet more urgently elsewhere, and must receive further training before undertaking this responsible task.

Beloved, whenever you are doubtful as to your course, submit your judgment absolutely to the Spirit of God, and ask Him to shut against you every door but the right one. Say, “Blessed Spirit, I cast on Thee the entire responsibility of closing against my steps any and every course which is not of God. Let me hear Thy voice behind me whenever I turn to the right hand or the left.”

In the meanwhile, continue along the path which you have been already treading. Abide in the calling in which you are called, unless you are clearly told to do something else. The Spirit of Jesus waits to be to you, O pilgrim, what He was to Paul. Only be careful to obey His least prohibition; and where, after believing prayer, there are no apparent hindrances, go forward with enlarged heart. Do not be surprised if the answer comes in closed doors. But when doors are shut right and left, an open road is sure to lead to Troas. There Luke awaits, and visions will point the way, where vast opportunities stand open, and faithful friends are waiting.
–Paul, by Meyer

Is there some problem in your life to solve,
Some passage seeming full of mystery?
God knows, who brings the hidden things to light.
He keeps the key.

Is there some door closed by the Father’s hand
Which widely opened you had hoped to see?
Trust God and wait–for when He shuts the door
He keeps the key.

Is there some earnest prayer unanswered yet,
Or answered NOT as you had thought ‘twould be?
God will make clear His purpose by-and-by.
He keeps the key.

Have patience with your God, your patient God,
All wise, all knowing, no long tarrier He,
And of the door of all thy future life
He keeps the key.

Unfailing comfort, sweet and blessed rest,
To know of EVERY door He keeps the key.
That He at last when just HE sees ’tis best,
Will give it THEE.
–Anonymous