Justification is by grace alone through faith in Christ alone, all to God’s glory alone. The Bible teaches that this faith that justifies is a GIFT from God (Eph 2:8,9; Phil 1:29) and not merely the product of man’s unregenerate nature which is still spiritually dead towards God in sin.
If faith is a merely a human choice, then it can be lost. This is true of a false and fraudulent kind of faith, which is temporarily enamored with the blessings of the kingdom (the idea of guilt removed, peace for a troubled conscience and such like) but which never can be characterized by a true and lasting love for the biblical Christ and the biblical Gospel.
In contrast, true saving faith is God’s gift to His elect people and is characterized by its enduring nature. Those who have made a profession of faith in Christ and walk away, never had the real thing. They never belonged to Him (1 John 2:19).