Our Scripture reading today is Romans 8:12-13.
Verse 13: "For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live."
The book of Romans was written by the Apostle Paul to Roman Christians.  It is important to understand these verses were written to born again believers.  Even after we get saved, living after our flesh will always end in death.  Our flesh brings absolutely NO life.  Sin always brings death whether we are lost or saved.  Thankfully, it is a different kind of death than the lake of fire mentioned in Revelation 20:14-15.  
God's Spirit takes up residence in us the moment we turn to Jesus Christ for salvation.  It is by His Spirit that we are able to die to the flesh and live by the Spirit.  In other words, we are saved by the Spirit of God and we must live the Christian life by that same Spirit.  The Holy Spirit will produce fruit in us to the glory of God.  Romans 6:22, "But now being made free from sin, and become servants to God, ye have your fruit unto holiness, and the end everlasting life."
Praise God for the freedom we have been given!  When necessary, repent for living in the flesh and pray for forgiveness.  Plead daily with the Spirit for His leading!