Some musings on union

God’s work is easy:
Then they said to him, "What must we do, to be doing the works of God?" Jesus answered them, "This is the work of God, that you believe in him whom he has sent." (John 6:28-29)

God’s commandment to Jesus:
For I have not spoken on my own authority, but the Father who sent me has himself given me a commandment—what to say and what to speak. And I know that his commandment is eternal life. What I say, therefore, I say as the Father has told me." (John 12: 49-50)

Faith leads to:
Whoever believes in me, as the Scripture has said, 'Out of his heart will flow rivers of living water.' (John 7:38)

The glory we have received through faith leads to oneness:
The glory that you have given me I have given to them, that they may be one even as we are one. (John 17:22)

Paul confirms this:
I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. (Gal 2:20)

Norman Grubb puts it like this:
Christ in you..John 10:10. This is the heart of the mystery of God in His dealings with men. Here we reach the summit of His ways. And coupled with this, the other side of the same relationship, we in Christ, as Paul adds: "that we may present every man perfect in Christ Jesus Jesus"(Colossians 1:28). But this exactly what we have seen eternal life to be: Three Persons dwelling in each other, in everlasting union and fellowship. Therefore when we are given the gift of participation in eternal life, we must of necessity share in this union, for there is only one life. Life is God in Three Persons dwelling in each other; the gift of life to us, therefore, is our introduction into this same mutual indwelling. It is the life of union, the one with the Other, distinct from each yet one in each other, interpenetrating. Mystery indeed, and foolishness to the natural man. The only life we know in our condition, in this three-dimensional world, is one separate from the other, communing with each other over space that divides us-I here, you there; and, as we shall see more clearly later. that same sense of distance and separation is what we carry over into our faith relationship with the Lord, and is the prime cause of our spiritual frustration and defeats.

Fred Pruit concludes like this:
It’s not really complicated. You died, He arose in you, and now a new life rises which is a union of He and you, and this new self which is you and He as one person is Who/who is now living. It comes out as you -- so you have risen this new self, joined to the Lord, who now expresses His divine life through and as your human life. You no longer struggle to be "divine-like," because He has assumed humanity in you; in order to reach your world as you. But it's us.

The mystery is summed up in Col 1:25-29:
….of which I became a minister according to the stewardship from God that was given to me for you, to make the word of God fully known, the mystery hidden for ages and generations but now revealed to his saints. To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is CHRIST IN YOU, the hope of glory. Him we proclaim, warning everyone and teaching everyone with all wisdom, that we may present everyone mature in Christ. For this I toil, struggling with all his energy that he powerfully works within me.

This is maturity in Christ:
Acknowledging that Christ is in you!