Rom 8:9 But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
Until a man has the indwelling Holy Spirit, he is a natural man, he is still in the flesh. No man is a spiritual man, a regenerate man until he has the indwelling Holy Spirit.
All scripture tells us a person receives the indwelling Holy Spirit AFTER first believing.
Eph 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
The scriptures do not say a person is regenerated to have faith at the same moment, the scriptures say AFTER a person believes they are sealed with the Holy Spirit.
Gal 3:2 This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith?
Paul's question demands the answer that these Galatians received the Spirit after first hearing and believing the gospel.
Acts 2:38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Peter's statement here is plain and unmistakeable, a person must first repent and believe on Jesus for the remission of their sins, and afterward they would receive the Holy Spirit.
Romans 8:9 shows that no man is "spiritual" until he has the indwelling Holy Spirit. Until a man receives the Spirit he is a natural man, he is still "in the flesh". But all scripture shows a man receives the indwelling Holy Spirit after they believe. Therefore, scripture proves the natural man has the ability to believe, and if he does he will receive the Spirit and become a "spiritual" person.
Jhn 7:38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
39 (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
Thousands of Jews believed on Jesus Christ before he was crucified, but none of them had the indwelling Holy Spirit. These were all natural men, they were in the flesh, yet they believed on Jesus. After Jesus rose from the dead and was glorified, afterward they received the Spirit.