A major area that separates those who are being saved from those who are perishing is the love of the truth. Truth sanctifies; it sets those who love and use it apart for the rewards of applying it to gain eternal life or better health.
Salvation is a process. Consider this: When God brought Israel out of Egypt, He redeemed them, but the process was not finished. It had only begun and did not end until they entered the Promised Land, a type of God's Kingdom. God intended the journey through the wilderness to prepare them for living in the land. However, a whole generation died in that process because they did not love the truth God gave them throughout the journey. The journey symbolizes the process of being saved.
Salvation is not religious rite, nor is it just a catchy theological term given to make people feel at peace. It is the experience of being saved from what would otherwise destroy us, which takes place between the time of our redemption and actually being spirit beings in the Kingdom of God. God is using His creative powers to get us to respond to truth. It does not matter what area of life or where the truth comes from. Truth is truth, but some truths are more important than others.
Verses 11-12 add more: "And for this reason God will send them strong delusion, that they should believe the lie, that they all may be condemned who did not believe the truth but had pleasure in unrighteousness." To those who will not yield to a love of truth, Paul warns, God will send a "deluding energy." As they reject the truth and continue in sin, a deceptive force will build and pull them deeper into it like a drug addiction. This parallels Romans 1:28, where Paul says, "God gave them over to a debased [reprobate, KJV] mind." This is what happens to people who leave the church: They continue to move further and further from the truth.