The Jews were given both the 10 commandments and a description of God’s backside by Moses. The verse also tells us why the Jews only know God by his backside.
Exodus 33 20-23
20 And he said, Thou canst not see my face: for there shall no man see me, and live.
21 And the Lord said, Behold, there is a place by me, and thou shalt stand upon a rock:
22 And it shall come to pass, while my glory passeth by, that I will put thee in a clift of the rock, and will cover thee with my hand while I pass by:
23 And I will take away mine hand, and thou shalt see my back parts: but my face shall not be seen.
This explains why the Jews could not identify Jesus with God even with Jesus standing in front of them.
John 14 7-9
7 If ye had known me, ye should have known my Father also: and from henceforth ye know him, and have seen him.
8 Philip saith unto him, Lord, show us the Father, and it sufficeth us.
9 Jesus saith unto him, Have I been so long time with you, and yet hast thou not known me, Philip? he that hath seen me hath seen the Father; and how sayest thou then, Show us the Father?
Because Jesus did not show them his backside and therefore they were unable to compare it to God’s backside.