Charles Spurgeon said, "Temporary faith is no faith at all." Jesus spoke of "those who believe for awhile, and in time of testing fall away" (Luke 8:13). Saving faith can stand the test, because it is an abiding gift of the Holy Spirit (1 Corinthians 13:13). Saving faith remains, abides, continues through all manner of testing.
Jesus taught that those who fall away only believe for awhile. This is recorded in the Parable of the Sower (Luke 8:11-15). The problem in this case is recognized in the person's heart. Those who fall away have a heart that has not been changed by the grace of God. It leads to apostasy, or falling away (1 John 2:19).
Those who are born again do not fall away, because God takes away the heart of stone and gives a new heart (Ezekiel 36:26). The new heart is like rich soil for the seed of the Gospel of Christ to bring forth fruit unto salvation. Those who are born again have a heart changed to become a new creation in Christ (Romans 2:28-29; 2 Corinthians 5:17).
When we are born again, our hearts are changed with new desires. The heart is the mind, will, and emotions, as the term is most often used in the Bible. God works in us "both to will and to do for His good pleasure" (Philippians 2:13). A new heart includes a will changed by God's grace. God began the work of salvation in us and continues unto completion (Philippians 1:6). Therefore, we do not fall away.
