The missing fourth word is the name of God. In line with normal Biblical style, we would have thought the verse would say, Vayikra HaShem el Mosheh – “And the Lord called to Moses”.
The problem is not apparent when the translators insert the word “He” in the verse, but how do we really know that “he” should have a capital letter? How do we know it was God who was calling? Maybe it was another human being, possibly Aaron!
A statement in the works of the Arizal, Rabbi Yitzchak Luria, is relevant. He says that a person who suddenly feels like crying on Rosh HaShanah knows by instinct that the Divine Judge is scrutinising him in the heavenly court. How can he be so sure? Maybe some other factor is at work! Yet the person concerned cannot be talked out of his conviction that he is on trial On High.
Back then to Moses. The verse does not identify who was calling to him, but he knew who it was. There are moments like that in everyone’s life, when we know we have so say, “Speak, Lord, for Your servant heareth” (I Sam. 3:9).