The physical body is flesh and it is sinful in nature, scripture says it is.

Colossians 2:11 In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:

The word "of" is defined as "belonging to". Therefore the verse is saying that sins belong to the flesh.

Why else would our bodies be called vile and need to be changed before we can go to heaven.

Philippians 3:21 Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself.

Romans 8:10 And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness.

Galatians 5:19 Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,

I am not sure how you can say that flesh/the body is not sinfull in itself. If I do with my hands that which is sinful... did my hands somehow not do the thing?

So why doesn't Scripture say that? Why does Scripture tell us these things: (Keep in mind this is just a listing of Scripture, not the context of them, that talks about the spirit of man)

Genesis 41:8 And it came to pass in the morning that his spirit was troubled; and he sent and called for all the magicians of Egypt, and all the wise men thereof: and Pharaoh told them his dream; but there was none that could interpret them unto Pharaoh.

If Pharaoh's spirit was dead... how could it be troubled?

Exodus 6:9 And Moses spake so unto the children of Israel: but they hearkened not unto Moses for anguish of spirit, and for cruel bondage.

If the children of Israel's spirits were dead... how could they it be anguished?

Deuteronomy 2:30 But Sihon king of Heshbon would not let us pass by him: for the LORD thy God hardened his spirit, and made his heart obstinate, that he might deliver him into thy hand, as appeareth this day.

If Sihon's spirit was dead...how could it be hardened?

Proverbs 20:27 The spirit of man is the candle of the LORD, searching all the inward parts of the belly.

Proverbs 16:32 He that is slow to anger is better than the mighty; and he that ruleth his spirit than he that taketh a city.

1 Corinthians 2:11 For what man knoweth the things of a man, save the spirit of man which is in him? even so the things of God knoweth no man, but the Spirit of God.