Simply put…this is just not the thinking of someone who has truly been saved.  One who has been freed from the power and penalty of their sin does not revel in being able to sin.  Let’s first look at Romans 6:1-2, “What shall we say then? Shall we continue in sin, that grace may abound? God forbid. How shall we, that are dead to sin, live any longer therein?”  Romans, chapter 5, speaks much about the grace of God that has been given to us.  Once we have realized the wonderful gift of God’s grace, how can we continue in sin?  GOD FORBID.  The one who is truly ‘dead to sin’ (read verse 6), does not delight in living in sin. 

We read in 1 John 3:9, “No one who has been born of God practices sin, because His seed remains in him; and he cannot sin continually, because he has been born of God.” (NASB).  The one who has been forgiven for their sins will not continue to live in sin.  No doubt, all believers do sin at times, but the Spirit, who indwells every believer, will convict our hearts for our sins and lead us to confess that sin to the Lord.  1 John 1:8-9 is written to the believer.  That says, “If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.”  The true believer will want to be cleansed from his sins, he will not enjoy wallowing in his sins.

Does the Bible teach us that if we are saved, then we will never lose our salvation?  YES, IT DOES!  Over and over, the scriptures assure us that once we are saved, the Lord will never take away our salvation.  We read in John 3:36, “He that believeth on the Son HATH EVERLASTING LIFE: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.”  This verse alone (although there are many others) should convince us of the security of our salvation.  To say that we HAVE everlasting life shows that we have it RIGHT NOW.  It is not something we hope to get someday, believers have eternal life RIGHT NOW.  The very word ‘everlasting’ shows that this life never ends.  If we could lose our salvation, then we never had everlasting life, for everlasting life (by definition) never ends.  (Read also John 10:27-29; 1 John 5:13; Romans 8:38-39, etc.)

If we are truly saved, we will be thankful for the eternal life that we have in Christ Jesus.  Our desire will be to live for Him, not to live in indulgence of sin and sinful pleasures.  2 Corinthians 5:17 says, “Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.”

I suggest that you ask your friend to consider 2 Corinthians 13:5, “Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates?”  (CC)  (509.6)