I am trying to master Paul's letter to the Ephesians, per the recommendation of David Powlison in his journal article Counsel Ephesians. The letter is truly fascinating in that it provides the reader a theological basis for the ethics to follow in chapters 3, 4, and 5. Ephesians 1:4 states, ...even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. So as followers of Jesus in a fallen world, we are challenged to live a life worthy of the calling, pursuing according to the Spirit the holiness each of us has been called to (Eph 4:1) and realized in eternity.
In 1 Cor 2:14, Paul alludes to the condition of humanity, noting that the natural man cannot understand the things of the Spirit. From this, we can gather that the "unnatural" man, or the man indwelled by the Holy Spirit, can indeed understand spiritual things. This reflects a change in his nature before the Lord, yet still stuck in a fallen world.
Redeemed humanity is changed by virtue of the Spirit's indwelling, which is why Paul can ask each of us to no longer walk in the futility of the Gentile mind (Eph 4:17) or for the thief to no longer steal (Eph 4:28) and people in general to avoid corrupted communications (Eph 4:29). I'm struck by the fact that some things are easily discernable, that we don't ask thieves to "pray about it" in terms of whether they will be obedient to God and avoid the sin of theft. We just expect obedience. We do the same thing with language. We teach that the use of certain profanities is inappropriate and so the practice should just simply be avoided. Obedience is something that we desire and can do because the Spirit lives within us. However, there are still those matters that are a bit more complicated, that scripture does not speak to directly. Those matters require that we try to discern what is pleasing to the Lord (Eph 4:10) and work a bit harder at figuring things out. The role of the mind cannot go unmentioned in our quest for holiness, and at the same time, it is not unspiritual to tap into our intellect--it, too, is part of God's creation.