"When you are baptized, partake of Holy Communion, receive the absolution, or listen to a sermon, heaven is open, and we hear the voice of the Heavenly Father; all these works descend upon us from the open heaven above us. God converses with us, provides for us; and Christ hovers over us--but invisibly. And even though there were clouds above us as impervious as iron or steel, obstructing our view of heaven, this would not matter. Still we hear God speaking to us from heaven; we call and cry to Him, and He answers us. Heaven is open, as St. Stephen saw it open (Acts 7:55); and we hear God when He addresses us in Baptism, in Holy Communion, in confession, and in His Word as it proceeds from the mouth of the men who proclaim His message to the people."
- Martin Luther (From 2 Sermons on the Saturday after St. Anthony's Day, 1538; Luther's Works, Vol. 22 : Sermons on the Gospel of St. John: Chapters 1-4. p.201 )