Albert Barnes on John 14:8

Lord, show us the Father. Philip here referred to some outward and visible manifestation of God. God had manifested himself in various ways to the prophets and saints of old, and Philip affirmed that if some such manifestation should be made to them they would be satisfied. It was right to desire evidence that Jesus was the Messiah, but such evidence had been afforded abundantly in the miracles and teaching of Jesus, and that should have sufficed them.