Salvation is offered to all. Yet, because of free will, man can choose to accept or reject it.
Next, after having accepted it, man can still lose it by willfully living in sin or by denying God.
Why? Because he always holds the power of choice, whether before or after conversion, having been given a free will by God.
God leaves the door open for reconciliation but if a sinful man refuses to repent, he cannot be saved. And God can do nothing about it (Matt. 23:37). This biblical teaching runs counter to Calvinism's "Irresistible Grace."
Why does God not immediately unleash his judgment on sinful man? Because God's justice is tempered/modified by His mercy:
1. "Righteousness and justice are the foundation of Your throne; mercy and truth go before Your face" (Psalm 89:14).
2. "And of His fullness we have all received, and grace for grace. For the law was given through Moses, but grace and truth came through Jesus Christ" (John 1:16-17).
3. "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (2 Peter 3:9).