All becomes clear when you consider the context, then link it with other things Jesus had already explained about his relationship with the Father. The context was the apostle Philip asking that they see the Father. Read from verse 8. This exasperated Jesus, for Philip had expressed his faith in Jesus as the promised Messiah the very first day they'd met, yet now, years later, he still didn't have experience of God as Father through all this time with the Son, "who is the express image of the Father". See John 1:45 & Col.2:2-10; The fulness of the Godhead dwelt in him bodily.
That is why Jesus rebuked Philip, saying, "Have I been so long time with you, and yet hast thou not known me, Philip? He that hath seen me hath seen the Father." (vs.9) To know Jesus is to know God as Father (vs.7). Then comes the verse you ask about. Matthew Henry's commentary on this is worth quoting.
"See here what it is which we are to believe (v. 10, 11)... as he had
said (ch.10 vs.30) "I and my Father are one". He speaks of the Father
and himself as two persons, and yet so one as never any two were or
can be. In knowing Christ as God of God, light of light, very God of
very God, begotten, not made, and as being of one substance with the
Father, by whom all things were made, we know the Father, and in
seeing him thus we see the Father. In Christ we behold more of the
glory of God than Moses did at Mount Horeb.
...He spoke not of himself only, but the mind of God according to the
eternal counsels... The Father is said to dwell in him ho en emoi
meno~n - he abideth in me, by the inseparable union of the divine and
human nature: never had God such a temple to dwell in on earth as the
body of the Lord Jesus - ch. 2:21." (Commentary, p1608 first column,
The Trinity doctrine may be viewed as the Father and the Son sharing the one, divine nature, with absolute unity of the Spirit in that nature. That is how Trinitarians can explain John 14:10, for while the Father remained in heaven during the Son's incarnation on earth, the Holy Spirit was their constant link, as it were. Thus we see all three Persons of the Godhead manifesting themselves distinctly at Christ's baptism. The man, Jesus, came up out of the water, the Holy Spirit appeared above his head as a dove, and God spoke in approval of his Son from heaven.
No. It is as the apostle John stated at the outset of that gospel - the uncreated Word of God, who made everything that was made, was with God in the beginning, and was God. Logically, the one who made everything that was made could not have been made himself. He left his glory in heaven to add human nature to his divine nature. All three Persons in the Godhead have their distinct roles and functions, and one relates to the others in special ways, yet they share that one, divine nature. One God, three Persons, from before creation into eternity.