My early months as a Christian were a joyous feast of fellowship. There was nothing I loved more than to be with my new brothers and sisters in Christ. Every believer I knew seemed so sanctified and intimate with the Savior. I actually felt intimidated by lives that were seemingly lived on another plane of righteousness to my own sinful struggles. But it didn’t take long before I discovered a sub-culture my Christian peers described as “backsliders.”
Few things can match the shock we experience when brought face to face with those who abandon the Christian faith. And there was nothing that could have prepared me for the grief of seeing hands once raised in worship, now deployed in satanic vices—backslidden from their former Christian faith.
I could not fathom why anyone would abandon eternal rewards for a short season of wicked pleasure. My Arminian pastor assured me that backsliding was the only possible explanation, and that our job was to “persuade these backsliders to come back to church and restore the salvation they’ve lost.”
Indeed some people were quite effective at retrieving backsliders and over the years I saw an endless stream of people who would gain their salvation, lose it, and re-gain it only to lose it again—rinse and repeat. My eyes were slowly opening to the reality that my church was actually a spiritual transit lounge for people in my city who periodically ventured into the kingdom of God. I could smell the problem but was unable to pinpoint the source. Did the Bible have an explanation?
“Backsliding” is an Old Testament term found in the prophetic books and used within the context of Israel’s unfaithfulness to God. John MacArthur describes it as “a word that the prophets used of apostate unbelievers.”  He concedes that Christians can backslide only in the sense that they “regress into a period of spiritual dullness or disobedience.” But he adds that such cases always incur God’s discipline (Hebrews 12:6–11) and produce repentance. 
That idea captures what most Calvinists mean if they use the term “backslider.” There is much that could be said about what constitutes a spiritual lapse, or how far you can go before you go too far. But the important principle to grasp is that the backsliding of a believer is always temporary and always involves God’s chastening which in turn produces repentance. It never means that their salvation was temporarily lost. (For further reading on this subject I would recommend two of John’s articles: Does Scripture Leave Room for Carnal Christians? and How Far Can Christians Go in Sinning?).
John argues that “backsliding” can never refer to a person who professes faith in Christ but lives in a “perpetual state of willful rebellion or ungodly indifference.”  Such people are not backsliding believers but rather false Christians who were never accepted by Christ in the first place (Matthew 7:21–23; 1 John 3:4–10).
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Source: Grace To You : Backsliding