My belief is that God exists beyond the realm of time. That He cannot change because time is something He controls, not the other way around. Once you understand that, you realize that God exists and that He sees the entire span of history as a timeline where He interjects himself as He chooses.
It is cautionary, though, to apply everything Old Testament to the Christian today because, in Christ, we are under a New Testament of salvation through faith rather than one of laws. We have freedom that the OT Hebrews did not have. Were that not true, the early Christian church would have led converts to exercise the same disciplines as the Old Testament Hebrews.
We have a freedom In Christ and with the aid of the Holy Spirit that was not available to the OT Hebrews.
I agree that the entire Bible points to Jesus but it would be wrong to apply Mosaic law to today's Christians.
Clearly, God exists in at least two dimensions of time (although "dimensions" is merely our term, not necessarily His). One easy way to visualize His interjecting Himself, as you describe, is to imagine God dealing with time not in a plane but as a globe. As our linear time progresses around its equator, God can drop down from His vantage point on its pole anywhere on that timeline, past/present/future. I'm sure it's an imperfect analogy, but I learned it from a Christian astrophysicist, so it has that credential, at least. If it's not helpful, just ignore it.