John 5:20

For the Father loveth the Son, and showeth him all things that himself doeth; and greater works than these will he show him, that ye may marvel.

The Father loveth the Son ... This fact should have been known to the priests, for God had so declared it vocally at Jesus' baptism.

And showeth him all things that himself doeth ... It would be difficult to imagine a more powerful claim to deity than this. As Barnes wrote:

From apostles, prophets, and philosophers, no small part of the doings of God are concealed. From the Son, nothing is hid. And, as God shows him all that is done, he must be possessed of omniscience, for to no finite mind could be imparted a knowledge of all the works of God.[11]

Greater works ... By this, Jesus meant that the Pharisees had by no means seen the exhaustion of his mighty powers. In the very next verse, he indicated that he would even raise the dead.