“For the mind-set of the flesh is hostile to God because it does not submit itself to God’s law, for it is unable to do so.” ‭‭Romans‬ ‭8:7‬ ‭HCSB‬‬ https://www.bible.com/72/rom.8.7.hcsb

The flesh is very selfish. It only wants to please its self. It only has thoughts of the next rush, whether it is from the next drug, drink, or physical pleasure. The flesh has the purpose to feel. It loves the next feeling and holds on to it. This is why God commands us to crucify the flesh.

“Therefore, brothers, by the mercies of God, I urge you to present your bodies as a living sacrifice, holy and pleasing to God; this is your spiritual worship. Do not be conformed to this age, but be transformed by the renewing of your mind, so that you may discern what is the good, pleasing, and perfect will of God.”

‭‭Romans‬ ‭12:1-2‬ ‭HCSB‬‬

https://www.bible.com/72/rom.12.1-2.hcsb

It is not only our job to crucify the flesh but it is our act of worship, service, to God. He wants us to deny the flesh and completely rely on the Spirit.