Living for God starts with thinking for God. It's as simple as that. If you would live for God, start by thinking for him or toward him. Notice what Paul says:
Romans 12:2: Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.
Two Ways to Live
Paul is presenting two ways to live. On the one hand, you can be conformed to this world, to have your life fit the overall shape and direction of the world - that is, for you to live like whatever part of the world you happen to live near. On the other hand, you can be transformed by the renewing of your mind, so that you might learn to discern the will of God, summarized in what is good and acceptable and perfect.
Why does it work this way? The fact that Paul says our minds need to be renewed implies not that we don't think but that there's something old about the way we think. There is something outdated, out of place, that no longer fits. Having our minds renewed is set together with not being conformed to the world, which seems to be the current danger. That is to say, an unrenewed mind results in a world-conformed life. Paul is calling for the inverse to happen. Saints should have a consistently renewed mind resulting in a transformed self.
It is worth noting, however, that there is no neutrality in the process. There is no one who can claim to have a mind unrenewed by Scripture and also a life unconformed to the world. What this person fails to recognize is that, insofar as their mind is unrenewed, they are the world. Sometimes people fail to understand that "the world" comes in many shapes, forms, and expressions. But it all has at least one thing in common: a shape, form, and expression of life that is not conformed to God's nature, design, and commandments.
Notice also that this mind renewal, by resulting in the transformation of the self, bears itself out in action. This is implied by Paul's mention of God's will, what is good and acceptable and perfect. It is insufficient to discern the will of God only. The expectation is that it will be obeyed! So it is that if you expect to live for God on the outside, you must think for Him on the inside. Your mind is the key to the motivations behind your actions. Change your thinking, change your actions. Living for God through Christ requires knowing the will of God. Thus right knowledge is indispensable to right living.
Thinking for God
If you want a transformed life on the outside then you must do the renovating work on the inside. If you would change the way you live then you must change the way you think. And if you would live for God then you must think for God. A person who looks like they live for God on the outside while they think like the world on the inside is merely play-acting. God is not interested in outward conformity but in total transformation. You cannot withhold your mind from God and expect to successfully live for him. Yet it is striking how many people do this.
It is perhaps equally striking that the unrenewed mind does not discern the will of God. Living rightly requires thinking rightly. Living for God begins with thinking for God.
One way to say this is to remark that what you are on the outside is not different from who you are on the inside. And there is no fooling the God who sees all. As humans, we seem prone to think that if we can look adequate on the outside then we can maintain our own supremacy in our thought life. We don't have to subject our minds to God if our outward behavior and manner of life are sufficiently conformed to his standards.
This completely misses the point! Paul's command here is not merely for the external behavior to be transformed, but the whole self. Can our thinking be separated from our conception of ourselves? Of course not! My perception is that we intuitively treat our own minds as sort of a sanctum sanctorum, a holy of holies, a sacred space that is devoted to our own personal use and which therefore is intensely personal. For some, though it seems not all, yielding our minds to God is almost a bridge too far. So often, we tend to operate as though we are the arbiters of what the will of God ought to be rather than as subjects called to be obedient to the will God has revealed.
And yet, this passage clearly states that the key to a transformed self is a renewed mind. It seems intuitively clear that we need the right thoughts to cultivate the right desires to make the right choices. This is because our minds are the interpreters and governors of our actions. We cannot settle for outward conformity when Scripture calls for inner transformation. Scripture makes clear that God doesn't.
Facing the Challenge
We must not make the mistake of believing that living for God through Christ is a function of merely external behavior. Living for God through Christ begins with thinking for God through Christ. Yet for many of us, there lingers a demand of the old self to maintain a vestige of control over our lives. Oftentimes, it seems, the mind is the last remaining holdout of our old nature, with certain thoughts, perceptions, presuppositions, opinions, perspectives, and the like dug in and entrenched like enemy forces opposed to the renewing power of Scriptural tenets.
For others, the case is different. They have long ago given up any autonomy over their minds and have fallen into a sort of laziness or intellectual servitude in the face of intellectual forces greater than their own. These are not so much actively opposed to the potential renovating power of Scripture as much as they feel helpless to comply, hopelessly subjected to a perceived inability to put it all together and order their thinking.
These aren't vying against Scripture for control over their minds; they gave up a long time ago. As a result, their conformity to the world is so complete as to be nearly unthinking. There is no vigor to their minds because any strength they had was shown to be inadequate long ago. The thought of wresting enough control to subject their minds to renovation by God's word is, frankly, intimidating and disturbing. Like some characters in The Matrix, they prefer the pill that allows them to go on living as though the possibility of a choice had never been presented to them. There is a thin veneer of plausible deniability in refusing to consider God's call to present our minds for renewal on the grounds that it sounds difficult.
In any case, the fact stands that living for God is inseparable from thinking for God. As our Spirit-wrought transformation began with the regeneration of our nature by God's power, the continued transformation of ourselves must begin somewhere. That starting point is our mind. If you want to live for God through Christ, begin with your mind.