Isaiah 40:18 To whom then will ye liken God? or what likeness will ye compare unto him?
This simple verse communicates a profound truth by way of a rhetorical question. Nobody can be compared to God. He is unique in His essence, quality, and character. He is the Creator and He is transcendent from His creation.
He is a spirit (John 4:4) and cannot be represented in a physical form. That is part of the reason that graven images were forbidden (Exodus 20:4), because no physical object can capture God’s glory.
But, you may object, Jesus is God in the flesh (Matthew 1:23; Philippians 2:6-8; 1 Timothy 3:16) and is the image of the invisible God (Colossians 1:15) and He has a physical form. True, but He did not reveal His glory (Isaiah 53:2). God the Father remains invisible to us.
As the verse implies, God cannot be compared to anything. He is without equal. There is only one God (Deuteronomy 6:4) and there is none like Him.