The Bible declares that there are only two conditions which human beings find themselves: Those who are 1) in the flesh, and those who are 2) in the Spirit (John 3:6). Jesus explains that those who are in the flesh "can do nothing" (John 6:63)... and "nothing" here in the context of HIs words includes the utter inability to exercise faith in Jesus Christ. How do I know? Emphasizing this very truth, the very next words of Jesus are “This is why I told you that no one can COME TO ME unless it is granted him by the Father.” (John 6:65) This demonstrates that the necessity of being "in the Spirit" before coming to faith in Jesus is not something up for debate among Christians but is an established truth of the Bible. No one can come to faith in Jesus while still in the flesh but must be made alive, quickened, regenerated. Therefore whoever disregards this, disregards not man but God, who gives his Holy Spirit to you.
"...no one comprehends the thoughts of God except the Spirit of God. Now we have received not the spirit of the world, but the Spirit who is from God, that we might understand the things freely given us by God." (1 Cor 2:11-12)
"That which is born of the flesh is flesh, and that which is born of the Spirit is spirit." (John 3:6)
"The natural person [those without the Spirit] does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned." (1 Cor 2:14)
"even when we were dead in our trespasses, [He] made us alive together with Christ" (Eph 2:5)
No one can say, 'Jesus is Lord,' except by the Holy Spirit." (1 Cor 12:3).
The Greek word for “flesh” in the New Testament is sarx, which often in Scripture refer to the physical body. However, the way Paul and Jesus are using it, it is not referring to the physical body (which of itself as created matter is not sinful). In fact, the Scripture's perspective of human nature sharply differs from that of Greek and Gnostic philosophy in that the Hebrew Bible says the physical and spiritual nature of humankind was good in its original state ... while the Greeks believed, rather, that freedom was escape from the physical body itself. Not only the doctrine of creation but the doctrine of the resurrection of the body denies this Gnostic idea entirely. Instead, "flesh" in the Bible, refers to our fallen nature (due to our choices) which is so utterly dominated by captivity to sin in every part (mind, soul, body) that nothing remains free from it's slavery. Only Christ can set it free (John 8:34-36). It must also be remembered that being "in the flesh" was not the condition of human beings in the original creation, but the result of the fall, where God has withdrawn his Spirit so that such ideas are rupulsive (John 3:19, 20). "Those in the flesh cannot please God" (Rom 8:8) and "without faith it is impossible to please him." (Heb 11:6) Therefore, those in the flesh cannot have faith. The Bible instead teaches that "the mind that is set on the flesh is hostile to God, for it does not submit to God's law; indeed, it cannot." (Rom 8:7)
Christ is the author and perfector of our faith ... the giver of new eyes, ears and hearts (Deut 29:4, 30:6). These are not self-generated and Christ is not improving upon the old man, but tearing down the whole edifice to build a new one, made after his own likeness. And just in case you are tempted to pridefully claim anything for yourself, when Peter declared that Jesus was the Christ, Jesus did not say "oh, great insight Peter. I will reward your faith with grace" No, he said, "Flesh and blood does not reveal this but my Father who is in heaven." God alone gets the glory for it is because of Him you are in Christ Jesus (1 Cor 1:29, 30).