Many people (including me) start out their Christian life in the Spirit and then later lose their focus and try to be perfected by the flesh. There by being frustrated and disappointed to see that they have lost the joy of their salvation.
We see a lot of joy and excitement in a newly converted Christian. But many old, "matured" christians do not have the same joy... Have you ever wondered why?
The answer is quite easy - The focus of a new Christian is in the Lord, not in the flesh.
When we are looking unto Jesus for our life and godliness we are walking by the Spirit. When we are looking to the law for righteousness and perfection we are walking by the flesh.
Bible says, if we have Christ we have everything we ever need for life and godliness. There is nothing we can add to that by our "works of the flesh".
His divine power has given us everything we need for life and godliness through our knowledge of him who called us by his own glory and goodness.- 2 Peter 1:3
Apostle Paul had many things to be boastful in the flesh-
circumcised the eighth day, of the nation of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as to the Law, a Pharisee; as to zeal, a persecutor of the church; as to the righteousness which is in the Law, found blameless. -Philippians 3:5-6
But he says he count all these as loss in order to gain Christ...
for we are the true circumcision, who worship in the Spirit of God and glory in Christ Jesus and put no confidence in the flesh - Philippians 3:3
If Apostle Paul says to put no confidence in the flesh, we better take it!
He calls the people who put their confidence in the flesh as "foolish".
Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh? - Galatians 3:3
We cannot add an inch of perfection by our work. period. We have the full perfection by inheriting the perfection of Jesus. We stand on His perfection, not ours.
We cannot trust our flesh, but we CAN trust the Spirit who dwells in us!
So lets put our confidence in the Spirit who lives in us... and walk by the Spirit...