Revelation 4:1
After this I looked, and, behold, a door was opened in heaven: and the first voice which I heard was as it were of a trumpet talking with me; which said, Come up hither, and I will shew thee things which must be hereafter. After this I looked, and, behold, a door was opened in heaven: and the first voice which I heard was as it were of a trumpet talking with me; which said, Come up hither, and I will shew thee things which must be hereafter.
The open door in heaven reveals heaven's unceasing ministry by which the divine Instructor directs workers on earth. Under God's guiding hand, different tasks enlist the energies of different heavenly messengers, like a wheel within a wheel. The voice that summoned John to come and be shown what must happen afterward speaks to every actor in God's work, girding and guiding even human instruments who have not known Him.
The open door also shows God revealing Himself through simple human means and agents who trust Him, even when others might overlook them. The invitation to come up is God's voice and Jesus' call to come up higher to a higher spiritual experience and to stand on holier ground every year of Christian life. That call means increasing more and more in faith, in righteousness, and in power while waiting, working, and praying for the coming of the Son of God. Heeding the voice and coming up higher brings the Holy Spirit, and souls are converted under that ministry.
Heeding it requires building on Christ Jesus as the prepared foundation, having the mind of Christ and living in Him, and living by every word from the mouth of God rather than by the counsel, advice, or praise of those who do not know God. It requires crucifying self so that principles, thoughts, and actions agree with God's words. Answering it means separating from idols and from everything unclean, worshiping God in spirit and in truth and in the beauty of holiness, and walking in the light where there is no occasion for stumbling. Those who teach God's word discern this call as they pray, behold Jesus, trust God, and live in communion with Him, and in response they cease to exalt themselves.