On the other hand, the person who is converted remains a sinner. He is a justified sinner, but a sinner nonetheless. John wrote to his fellow saints, "If we say we are without sin, we deceive ourselves, and the truth is not in us" (1 John 1:8). Paul exhorted Timothy, "exercise yourself toward godliness" (1 Timothy 4:7). Paul describes the believer’s constant struggle against sin and toward godliness in Romans 8:13 when he writes, "For if you live according to the flesh you will die; but if by the Spirit you put to death (the AV reads "mortify") the deeds of the body you will live." As the Puritan John Owen put it, either we will kill sin or sin will kill us.
In this age, the saint is constantly at war against sin. In the age to come, he attains the final state of glorification, when by God’s grace all sin is overcome.
In a section of his book Overcoming the World (P&R, 2005) with the heading "Cultivating Holiness as a Constant Struggle" Joel Beeke gives this analogy:
I once read of a missionary who had in his garden a shrub that bore poisonous leaves. He also had a child who was prone to put anything within reach into his mouth. Naturally, the father dug the shrub out and threw it away. The shrub’s roots, however, went very deep. Soon the shrub sprouted again. Repeatedly, the missionary had to dig it out. There was no solution but to inspect the ground every day and to dig up the shrub every time it surfaced. Indwelling sin is like that shrub. It needs constant uprooting.
May God give us the strength and endurance needed to win the constant battle for holiness.
Grace and peace, Pastor Jeff Riddle