It shows the relationship between God the Son and God the Holy Spirit, just as the following shows the relationship between God the Father and God the Son, all three of whom are omnipresent.
Acts 3:20-21Proceed forth from the presence of God the Father is what you do when you are sent by Him. You go from heaven to earth to do as you have been commanded.
20 And he [God the Father] shall send Jesus Christ, which before was preached unto you:
21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
John 8:42 Jesus said unto them, If God were your Father, ye would love me: for I proceeded forth and came from God; neither came I of myself, but he sent me.
John 15:26 But when the Comforter is come, whom I will send unto you from the Father, even the Spirit of truth, which proceedeth from the Father, he shall testify of me:
These are among a multitude of verses that show that the Father, Son, and Holy Spirit are three Persons who are One, having a perfect unity of heart, mind, purpose, thought, action, etc.
Three Persons who are One is substance as well?
pony