How can Jesus be in the Father and the Father be in Him?     
Understand who the Father is.     He is a Spirit.     He is the Holy Spirit.     The Holy Spirit fills the universe and beyond.     But He birthed the body of Jesus and annointed Him to be Messiah - He filled the body of Jesus.     

Jesus spoke what the Holy Spirit inspired Him to speak.     Jesus reached out to heal and deliver those whom the Holy Spirit empowered Him to bless.     

Just as the disciples and others of Jesus` day could not look past the physical form of Jesus and see the Father, likewise today, people cannot see past our physical form to see the Father in us.     

What is even worse is that many of us cannot look past our own physical form to realize Christ in us the expectation of the Father`s glory being manifested in and through us.     

Greater works shall we do because the Father has made His abode in us.     We are filled with the Holy Spirit.     

---

Father is a role.     It is not the name of a being.     The name of the Father is Christ Jesus.     (For that matter, the name of the Holy Spirit is Christ Jesus).     But Jesus was clarifying how He, as a man, was able to do what He did and say what He said.     

The Holy Spirit is the Father of Jesus.     He is the one who impregnated Mary.     He is the One who inspires and implements the Word.     

So, Jesus being the Word speaks and interacts with those in the Physical Realm, while the Holy Spirit from the Spirit Realm (Heaven) inspires Jesus to speak and then performs the works that Jesus does.     

The Holy Spirit and the Word are One.     You cannot separate them.     If you try to you will either have the Word or the Power and neither will be effective.     The Word speaks the purpose, while the Power achieves the purpose.     The Holy Spirit and Word are inseparable.