For Him to be seen everywhere...I think He's God, and He might do it any number of ways.

The earth could flatten for a moment, and people be able to see all the way to the Mount, just 'cause God wanted to awe them...or any number of things could happen...I think that whoever is here on that day will be in awe of Him however it takes place.
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...they received the word with great eagerness, examining the Scriptures daily to see whether these things were so.
Acts 17:11
Be diligent to present yourself approved to God as a workman who does not need to be ashamed, accurately handling the word of truth.
2 Tim 2:15