If you are trying to understand the theophonic appearances of God in the O.T, in light of John 1:18, you need to understand the meaning of the word John uses.
In verse 18, John says,
“no man has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him.”
There are two words that need to be addressed in this statement by John. The first is the word “ἑώρακεν” that is translated here as "seen" in most of the English translations. The word is third person singular of “ὁράω” which, according to Thayer, has three basic definitions. First, it means to see with the eyes. Secondly, it means to see with the mind, to know, to perceive. Thirdly, it means to become acquainted with through pragmatic experience (The 1981 New Thayer’s Greek English Lexicon, p 451).
If John is arguing from the first definition, this needs to be understood in the light of pragmatic Old Testament examples. We know from the many examples of theophonic manifestations in the Old Testament that God has repeatedly presented himself to man in a number of ways. At times, God availed himself only to man’s auditory senses. He spoke to Adam, to Cain, to Noah, to the Hebrew patriarchs, to Moses, to the prophets, and to others. Sometimes he visited himself upon man in the form of dreams or visions as to the prophet Isaiah in Isaiah chapter six. Other times, he appears as objects such as the cloud or the pillar of fire that went before Israel in the wilderness. Still, there are other times when he visited man in human form. There are some eight accounts of this type of theophany found in the Old Testament.
The second word is “ἑώρακεν”. If “ἑώρακεν” is to be understood as an intellectual limitation, this would seem to fit better with the closing statement of this prologue. “He has explained him.” The Greek word “ἐξηγήσατο” means to set forth in detail, to set forth in language, to make known or to reveal (George V. Wagram’s Analytical Greek Lexicon of the New Testament, 1983). This is the etymology of our word ‘exegete’. In other words,
“No man has understood or comprehended God at any time. The only begotten Son who is in the bosom of the Father, he has EXPLAINED him.”
The Logos presents God to the mind of man through the medium of human language in such a way that man is now able to understand something of the nature and character of God that he could never know from his observation of the natural world. Only the one who came out of the very presence of God could have done this.