51“And he said to him, “Truly, truly, I say to you, you will see heaven opened, and the angels of God ascending and descending on the Son of Man.”
The Holy Bible: English Standard Version. (2016). (Jn 1:51). Wheaton, IL: Crossway Bibles.
When did Nathanael see the heaven opened, and when did he see the angels? There are only two instances in the New Testament telling us that the heaven opened. The first was: when Christ stepped out of the Jordan after His Baptism by John, we read that the heaven opened, the Holy Spirit descended in the form of a dove, and the Father’s voice was heard (Matt. 3:16–17). The second was: as we read in Matt. 17:1 ff., the heaven opened when Moses and Elijah appeared to Christ and three of His disciples on Mt. Tabor. A white cloud overshadowed them, which made their faces and their garments as lustrous as the sun. Only the three apostles saw the heaven opened there; Nathanael was not present, nor was anyone else. Therefore our text must have a special meaning. Christ Himself interprets it. As we see,. The evangelist does not mention a ladder but merely says that the angels of God ascended and descended upon the Son of man. Therefore this story must be interpreted spiritually. The vision which the patriarch had on the site where Jerusalem was subsequently built points to Christ. It has never again been closed since Christ’s Baptism in the Jordan; and it will never again be closed, hidden though this sight is from the physical eye. When heaven is open and God the Father addresses us, we note this only with our spiritual sight. Before the advent of Christ heaven was closed, and the devil had full sway; but The Heavenly Father still addresses these words to us: “This is My beloved Son!” He will continue to do so until the Day of Judgment, nor will heaven ever be closed again. 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.
Luther, M. (1999). Luther’s works, vol. 22: Sermons on the Gospel of St. John: Chapters 1-4. (J. J. Pelikan, H. C. Oswald, & H. T. Lehmann, Eds.) (Vol. 22, pp. 201–202). Saint Louis: Concordia Publishing House.