Concise Bible Dictionary:
There are four Hebrew words applied to backsliding.
1. sug, “to go back”: “the backslider in heart shall be filled with his own ways,”‘ instead of God’s ways (Prov. 14:14).
2. sarar, to act like a refractory heifer, that will not draw regularly in the plow: to which Israel is compared (Hos. 4:16).
3. meshubah, “a turning away, apostasy.” (Jer. 2:19; Jer. 3:22, 6-12; Jer. 5:6; Jer. 8:5; Jer. 14:7; Hos. 11:7; Hos. 14:4).
4. shobeb, “rebellious, backsliding.” (Jer. 3:14, 22; Jer. 31:22; Jer. 49:4). The last three words are all used of backsliding Israel. We do not find the word “backslider”‘ in the New Testament but the same sin is there pointed out, for instance the drawing back which may lead to perdition as in Hebrews. 10:38-39. See APOSTASY.
From Anstey’s Doctrinal Definitions:
The Bible speaks of two kinds of departure from God––apostasy and backsliding. Both are bad, but one (apostasy) is infinitely worse. A believer can never apostatize, but he surely can backslide, if he is not careful in his walk. If a believer does backslide, there is a remedy (confession and repentance, whereupon he is restored to the Lord – 1 John 1:9), but if a merely professing believer apostatizes, there is no remedy (Heb. 6:4-6). (See Apostasy.)
The words “backsliding” and “backslider” are not found in the New Testament, but this kind of sad departure from God surely is mentioned (Mark 14:30; James 5:19). It has to do with a believer becoming careless in heart as to his communion with God (Prov. 14:14), and if this is not judged, it will result in a wayward walk from the Lord. The work of Christ as an Advocate brings the backslider back. The restoration of the backslider involves repentance and the confession of sins to the Father (1 John 1:9). (See Advocacy.)
It is important to understand that backsliding does not affect a believer’s standing before God; hence, the backslider does not lose his salvation. But as Proverbs 14:14 indicates, the backslider pays a heavy price for his waywardness in reaping what he has sown (Gal. 6:7-8; Prov. 13:15). If we allow sin to go unjudged in our lives, there will be disastrous results:
• Our link of communion with God will be broken (Rom. 8:13).
• We acquire a bad conscience which will result in a lack of confidence in prayer (1 John 5:14-15).
• We will lose spiritual energy.
• We will lose discernment (Hos. 7:8-9).
• We may become a slave to the sins that we allow in our lives (1 Cor. 6:12).
• The chastening hand of God will be laid upon us in order to turn us around (Heb. 12:6). Such chastening could even go to the extent of being taken away in death prematurely (Eccl. 7:17; 1 Cor. 11:31-32; James 5:20; 1 John 5:16).
• We spoil our Christian testimony before the world (Gen. 19:14).
• We will lose a reward that the Lord intended for us to have (1 Cor. 3:13-15; 2 Cor. 5:10; Rev. 3:11).