Question: "If Christ died for all our sins, INCLUDING UNBELIEF, then why are there people who will be in the lake of fire?"
It is a legitimate question indeed.
The Bible says: "Whoever believes/trusts in Him shall not perish but have eternal life" and that "he who does not believe/trust is condemned already, because he has not believed/trusted in the name of the only begotten Son of God."
Now, if the Lord Jesus died for all our sins, including the sin of not believing or not trusting in Him, then why do people still perish? Did not His death on the cross pay for the sin of unbelief also?
Again, the answer lies in the provisional nature of Christ's death on the cross. The Lord Jesus Christ is provided for all and offered to all. Picture a cleansing fountain placed by God in the center of a sin-laden world.
And hear God calling out to everyone to come to the fountain, plunge in it, and be cleansed. The fountain has the potential to cleanse all kinds of spiritual dirt in the world. It was given for that very purpose. It is sufficient for all, but only those who come to the fountain, experience its cleansing.
Payment for all our sins is provided and offered in Christ, since He Himself procured for us a provisional payment for our sins when He died on the cross. But only those who are "in Christ" actually experience its blessing.
Eph 1:7 IN HIM we have redemption through His blood, the forgiveness of sins...
Yes, but are you IN HIM, by coming to Him in faith?
1Jo 5:11 ...God has given us eternal life, and this life is IN HIS SON.
Yes, but are you IN HIS SON, by coming to Him in faith?
Ro 8:1 There is therefore now no condemnation to those who are IN CHRIST JESUS
Yes, but are you IN CHRIST JESUS by coming to Him in faith?
There is a fountain of life and forgiveness provided for us all, but are you in the fountain? Have you plunged yourself in it? The mere presence of the fountain does not automatically cleanse you. You must be in it.
There is an ark provided by God for us all, but are you in the ark? The mere presence of the ark does not save you from the flood of judgment. You must be in it.
