With regards to Christ appearing in the Old Testament, some would argue that it is the Father that appears and not the Son, but there are several proofs which state it was Christ which appeared. One such proof is that the Bible teaches that God is invisible and therefore sent the Son to be visible on His behalf. Also, we cannot come to the Father without first going through Christ, so we cannot see God directly. Some examples of where Christ appears on behalf of the Father in the Old Testament would be many cases where "the angel of the Lord" appears, the angel of the Exodus, the "man" who wrestles with Jacob, the "man" who appeared to Abraham, the "man" who appeared to Joshua, and the angel of the Lords appearance to Samson. The Old Testament contains hundreds of prophecies regarding the coming of Messiah to the earth. Through these prophecies, we know that Jesus was the Messiah because He fulfilled every one. He fulfilled all of the Old Testament prophecies pointing to Him. Thus, when we look at prophecies about our future, we also know they will be fulfilled exactly as God has said, because there are five times more prophecies about His return to earth the second time than there are about His coming the first time. So this means the return of Christ is something the Bible really emphasizes.
In conclusion, man can never really know the nature of God. All we can do is look at the evidence that is around us and try to put what we know and feel into human terms. We can never do justice to God by describing how we think He really is, but because He gave us the ability to think and reason and know Him, all we can do is try our best and live for the glory of God.