You must work out your own salvation in fear and trembling; for it is God who works in you, inspiring both the will and the deed, for his own chosen purpose. Phil. 2:12, 13, N.E.B.
Let's imagine a large chart with three positions clearly marked on it. These three positions portray three stages of our Christian walk.
Start down in the lower left corner of the chart with Position 1 and label it "Selfish will." This represents pre-Christian values. It's the independent, "I'll-do-what-I want" will of the rebel. This needs no explanation; we've all been there.
Next draw a sweeping line (like the arc of a pendulum) to the far right of the chart and mark it Position 2. Give it the title "No will of my own." This is the experience of many new Christians who remember with tears the days of their independence from God. With absolute sincerity they vow never to move outside God's will. When asked what they might wish to do, they would say, "It's not what I want, it's what God wants that matters; I must crucify myself."
For those at stage two, any thought of doing what one wishes to do, brings back painful memories of their pre-Christian days, and they recoil at the idea. Obedience means meekly submitting to whatever God wants, interposing nothing at all of one's own wishes and desires. God originates all instructions and plans. Interestingly, God--and not the individual--is then accountable for what happens!
Once again, use your marker to draw a line to the top and center of the page, and locate Position 3. Give this one the label "Sanctified will." This represents the position of the mature Chrstian, the one whose values and goals have been edified by Christ, who indeed has the mind of Christ. This is the one who finds, to his sheer delight, that what he most wants to do is the very thing that Jesus wishes for him to do.
God designs Position 2 to be only transitional. He does not wish to do our thinking and choosing for us. Rather, He wishes to equip us to do our own best thinking and to bear accountability for our own choices. Paul was presenting this idea when he told the Philippians to trust the working of God in their own hearts and--with due respect and reverence--go ahead and make their very own decisions.