Cult of Calvinism & Galatians

Paul decisively refutes OSAS and "Perseverance of the Saints" (not quite the same thing). He warns born again believers who God had called, and who had received the Holy Spirit, that if they started in the Spirit but ended in the flesh, they will not inherit the Kingdom of God. If such a thing could never happen, Paul would not bother to warn these born again believers. Now ask how it is that a true believer can fall short of inheriting the Kingdom of God.

Believers must abide/remain in Christ or the will not inherit the Kingdom of God. God is not mocked: a man will only reap what he has sown and to believe otherwise is to be a deceived person. Gal 6:7-8. See also 1 John 3:6-9 and James 1:22.