Jesus, just prior to this, told His disciples the way to the Father's house where He will be preparing a place for them. Now Christ assures them that they have known and seen the Father through Himself. There is a complete unity between the Father and the Son. However, Philip and the apostles don't find this sufficient and want an immediate display of God Himself. Jesus responds with a rebuke that is tinged with sadness. They have been with Jesus this long and they still don't see it. Jesus's words, person, and works are not insufficient to show the Father but Philip and the apostle's vision is insufficient to see the oneness of the Father and the Son. They don't realize they have known and seen God this whole time in Christ. He says "Believe Me that I am in the Father and the Father is in Me." This doesn't simply mean "trust Me." But it means that the Trinity is an absolute must-believe aspect of following Christ. They also ought to believe not just on the basis of His words but His works. And it's not just the power behind the miraculous signs but what the signs also signified about who He is and what He's come to do. He is God in the flesh. And then Jesus speaks of His relationship to His disciples. Those who believe in Him will do greater works. It's not that Christians will have a power greater than Jesus to raise the dead or heal or calm a storm; the key is in the phrase "because I go to the Father." The works are still Jesus's and the disciples of Christ will ask to do them in His name and only what He wants to be done will be done. The works are greater because they are after the cross and resurrection but they are not greater than Jesus's.
