...That they all may be one, as You, Father, are in Me, and I in You. (John 17:21)
What, then, is union with Christ? It is union with Him as the new creation, as the new creation Man; union with Him in the Life which is the life of the new creation by the Spirit of Life. What is the meaning of that union? It is that only by such union can God's works be done. What governed Him in relation to the Father governs us. Nothing can be done except on the ground of this union. It is not a matter of action, or of undertaking for God, however well intentioned. What we see as seeming necessary to be done for the Lord's glory is not the criterion of service. Many things are embarked upon by the mere simple, though honest and sincere, judgment of the heart, when confronted by what is judged as something to be done for God, something needing to be done. A tragic situation, for example, calls for action; we have the means to meet that situation, and so we embark upon it for the Lord. A vast variety of undertakings have been embarked upon in that way, from that basis, and the Lord Jesus in this chapter says, "No! Not so!" He is not governed by the apparent demand of a situation. He is not governed by the impact of things upon Himself, as calling for an undertaking.
With Him it is a question of what God is doing, and doing just at the particular time. With one object, God does different things at different times, and has a different emphasis from time to time, and those who are really in union with Christ have to be governed by that which Christ at that particular time is Himself undertaking, is giving Himself to: "...what things soever He doeth these the Son also doeth in like manner." It is a matter of what God is doing, and life-union with Him in Christ for the accomplishment of that.
By T. Austin-Sparks from: The Meaning of Divine Life - Chapter 3