"So all this was done that it might be fulfilled which was spoken by the Lord through the prophet, saying: 'Behold, the virgin shall be with child, and bear a Son, and they shall call His name Emmanuel,' which is translated, 'God with us.'"
When we say Jesus in the flesh was, "God with us", what does that mean? We simply must look at the way Jesus had previously been revealed prior to His birth to understand better what His incarnation meant. To begin our quest, we look briefly at John 1:18 as the Rosetta Stone to interpret for us how we should understand the various appearances of God in the Holy Scriptures:
"No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him."
Whew! That's worth re-reading. I'll insert brackets to assist:
"No one has seen God at any time [if you're not Trinitarian, you're in trouble]; the only begotten God [neither the Father nor the Holy Spirit are ever described as having been "begotten" so, that leaves You Know Who] who is in the bosom of the Father [hmm... we have God with God and God at the side of God... sounds a lot like John 1:1-2 here], He [Jesus is the Son of God which logically makes Him "the only begotten God"] has explained [revealed] Him [the Father]."
Simple enough, right?
Well, it seems pretty straight forward from this verse of scripture, almost everything I used to think about God in the Old Testament was wrong. I used to believe that every time God spoke/appeared or was otherwise revealed before Christ's birth, it had to be The Father. It's so strange because if you had asked me whether I believed in Christ's existence before His birth, I would have said "yes". But then, I'd go along making impositions on the Bible as if I denied it. Anyways...
John 1:18 appears presents a problem when we consider texts like, Genesis 18:1; Exodus 24:9-11; Numbers 12:6-8. How can it be that "no one has seen God" when these OT passages clearly speak of persons seeing God. Plain and simple, the Bible says that Abraham saw Yahweh. Up to and at least 70 elders of Israel saw Yahweh. Then we find that Moses sees Yahweh's form. This is especially confusing when Jesus tells us in John 4:24 that God is a Spirit (what form does a spirit have?) and 1st Timothy 6:16 says that seeing God hasn't happened nor CAN it happen. How do we answer this question?
Well, like any kid who's ever been to Sunday School knows, when you can't answer the question, just say "Jesus". And in this case, it's not just the trite thing to do, it's the most profound answer possible.
As one who holds to the doctrine of the Trinity, I believe Jesus is God. But I don't believe that Jesus is the Father. In the OT, there weren't any obvious or plain distinctions between the Father, the Son, and the Holy Spirit. Perhaps this is in part because God's first step in revealing Himself is was to impress the singularity of His being upon His people. We can see that being essential because of the polytheistic systems of religion that had to be avoided and denied by Israel in order that they would be the Lord's people.
But the revelation of Jesus requires a distinction between persons in the Godhead. In NT talk, "God" is almost always a reference to the Father and "Son" is naturally a reference to Jesus. So we find that Jesus is SENT by God although He is God (even OT passages hint to this kind of distinction, see the speaker in Zechariah 2:8-11).
Therefore, when we see a passage like John 1:18, declaring that no one has ever seen God it says plainly that those who saw Yahweh didn't see the Father, but they saw the Son. Jesus is the One Abraham, Moses and the 70 elders saw. Jesus is the One Who has explained and revealed the Father, not only in the NT but in the OT as well. . John 1:18 has not introduced a contradiction, but a clarification.
So all those times God appeared in the Old Testament, that was Jesus? Yes. All the judgement, all the fire, all the thunder-- that was Jesus? Yes, yes, and yes. Amazingly, "God with us" did not come to kill as many had feared (see Exodus 20:18-19). Emmanuel came to save us.