Rom 8:5 For they that are after the flesh do mind the things of the flesh; but they that are after the Spirit the things of the Spirit.
6 For to be carnally minded is death; but to be spiritually minded is life and peace.
7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be.
8 So then they that are in the flesh cannot please God.
None of this scripture says a man is unable to think spiritually. That is why I brought up Matthew 26:41
Mat 26:41 Watch and pray, that ye enter not into temptation: the spirit indeed is willing, but the flesh is weak.
No believer had received the Holy Spirit yet, so Jesus must be speaking of his disciples natural spirit here, and Jesus said they were WILLING to obey him. This is the same thing Paul describes in Romans 7. I believe Paul is describing himself before salvation in Romans 7 because he said sin had slain him and that he was sold under sin, neither of which are true of a saved person.
Matthew 26:41 is important because it shows an unregenerate man is not flesh only, but he is spirit and soul as well, and that the spirit indeed can be willing to believe and obey God.
You choose to ignore this scripture because it refutes your view.
All that is the human condition before belief is fallen. That includes the spirit, the mind, the soul, the strength.
That fallen is replaced as Paul stated that the believer is:
17 Therefore if anyone is in Christ, he is a new creature; the old things passed away; behold, new things have come. 18 Now all these things are from God, who reconciled us to Himself through Christ and gave us the ministry of reconciliation, 19 namely, that God was in Christ reconciling the world to Himself, not counting their trespasses against them, and He has committed to us the word of reconciliation.
Not that the fallen nature is made of none effect - for this thread discussion of Romans also has acknowledge that there is a "therefore" referring back to the great conflict that every true believer engages between the will of the flesh and the will of the new nature.
Further in your attempt to use Matthew as a foundational text in support of your view, you neglect that Christ was present with them and actively protected them as it states in: John 17
6 “I have manifested Your name to the men whom You gave Me out of the world; they were Yours and You gave them to Me, and they have kept Your word.7 Now they have come to know that everything You have given Me is from You; 8 for the words which You gave Me I have given to them; and they received them and truly understood that I came forth from You, and they believed that You sent Me....
11 I am no longer in the world; and yet they themselves are in the world, and I come to You. Holy Father, keep them in Your name, the name which You have given Me, that they may be one even as We are. 12 While I was with them, I was keeping them in Your name which You have given Me; and I guarded them and not one of them perished but the son of perdition, so that the Scripture would be fulfilled....
15 I do not ask You to take them out of the world, but to keep them from the evil one. 16 They are not of the world, even as I am not of the world...
These verses indicate that Christ was active in protection and thwarting attacks (because He is the Word) just as Paul states when the believer is dressed in the armor of God extends the Word for protection.
Did not Christ declare that while the light was with them they should walk in the light? John 9:
"5 While I am in the world, I am the Light of the world.”
Did not Christ state that when He left another would be sent to take His place? John 14
16 I will ask the Father, and He will give you another Helper, that He may be with you forever; 17 that is the Spirit of truth, whom the world cannot receive, because it does not see Him or know Him, but you know Him because He abides with you and will be in you.
Perhaps you can find support in other Scriptures, but the disciples, Christ, and work of the Holy Spirit given in the above passages would not lend support.