For the one who sows to his own flesh will from the flesh reap corruption, but the one who sows to the Spirit will from the Spirit reap eternal life.Galatians 6:8(NASB)
The word 'flesh' has many meanings and can refer to different things depending on the context... but in this verse the word 'flesh' is referring to the old sin nature - the fallen, fleshly, egocentric nature we inherited from Adam. In this passage 'flesh' refers to the old sinful self - 'the old man' as the Bible calls it.
Adam was the federal head of God's creation. It was the first creation - the old creation which became a fallen creation. When Adam sinned, man died spiritually, leaving every member of humanity dead in trespasses and sin. Man's body also started to die immediately and man's soul was corrupted and tainted with sin... such that man knew what was good yet was unable to do it... and man knew what was evil but was unable to avoid it.
Works of the flesh are totally rejected by the Lord. Good deeds that are carried out by the old sin nature, however commendable they appear to be, are utterly rejected by God. The only way that man can return into fellowship with his Creator, is by becoming part of His new creation - where Christ is the federal Head of an entirely new race of humanity.
Once we have been saved by grace through faith in Christ, any good works that we undertake are to be done through the new, Christ-given nature which we receive at salvation, and not the old, sin nature which was imputed to us due to our membership of the first creation in Adam. When we were born into that old sin-ridden creation, we received an old sinful nature. But once we are born from above, we became part of a new, perfect creation with a new nature and a new life in Christ.
Once we have been saved... everything and anything that is connected with the first creation and our old sinful nature, is totally and utterly rejected by the Lord. Any good works that are undertaken by means of our 'old man' are unacceptable to the Lord and can never honour His name. Any good actions or kindly deeds that are carried out in our original, fleshly sin nature which we received from the first Adam, will never, ever be acknowledged or accepted by the Lord.
There is nothing we can do to commend ourselves to the Father. There is no work we carry out in the flesh that can merit God's approbation. There is no ritual we can perform to gain God's approval. If our sacrifices are selfish, our self-denials are fleshly, our prayers are self-righteous, our preaching is self-elevating, or our good words are self-seeking, then God cannot and will not have anything to do with them because they emanate from the old sinful nature. They are works of the flesh and will be burned up as wood, hay, and stubble at the Bema Seat of Christ.
The Christian life must not be focused on self, but on Christ. We are to live in the 'not I but Christ' realm. We are to die to our own sinful desires, lustful leanings, and self-elevating egocentricities. We are to keep the fleshly self, with all its pretence and self-deception, firmly nailed to the Cross - and we are to live our life for Christ alone.
When the Lord Jesus won the victory on the Cross, we received a new life by faith. At salvation we were removed from the old creation in Adam and placed into the new creation in Christ. The sinful, fleshly old man will seek to reassert its supremacy while-ever we are in our human body of flesh and blood, but each fleshly uprising must be deactivated as we deny self, take up our Cross, and take every thought captive to Christ.
As believers, we still retain our freewill, but in Christ we have received power over that old, fallen, sin nature as we die to self and live for Christ alone. If we permit the old sin nature to mount the throne of our life, we dishonour the Lord and will reap the bitter fruit of sinfulness, but if we keep the old man nailed to the Cross and live for Christ alone, we will reap the everlasting fruit of righteousness: "For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life."
Heavenly Father, thank You that I am part of the new creation in Christ and have been freed from the ravages of sin, death, and hell, by faith in the shed blood of Christ on Calvary. Father, I want to live my life in spirit and truth and keep the old sin nature out of commission and nailed to the Cross. Help me to honestly recognise any fleshly tendencies to which I may cling and keep me, I pray, from sowing to my flesh. Rather, I ask that in the power of the Holy Spirit, I may sow to the Spirit and live my life in humble submission unto the Lord for His praise and glory. In Jesus' name I pray, AMEN.