And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world. 1 John 2:2When the Apostle John wrote this, Christ had now died, resurrected, and ascended into heaven. We see something else here: Jesus provided a propitiation for the sins, not just of believers, but for the sins of the whole world. Does that mean that everyone receives that propitiation? No. In Romans 3:25 we saw that God only remitted the sin of those with faith in His blood.
Does it seem clear to you from 1 John 2:2 that Christ was a propitiation for everyone, including unbelievers? And in light of Romans 3:25 that He satisfied His Father's righteous demands for everyone who ever lived? That seems like the plain reading of Scripture to me. And then I read these:
Jesus died for the ungodly.
For when we were yet without strength, in due time Christ died for the ungodly. Romans 5:6Jesus died for all.
Who gave himself a ransom for all, to be testified in due time. 1 Timothy 2:6 For therefore we both labour and suffer reproach, because we trust in the living God, who is the Saviour of all men, specially of those that believe. 1 Timothy 4:10Jesus died for the unbeliever, the apostate, the one who has permanently turned away from Him.
But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them. 2 Peter 2:1Jesus died for me.
I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me. Galatians 2:20Jesus died for you. Will you believe in Him alone for your salvation?
 "Remission" in Rom. 3:25, the word paresis, means "a passing over" or "overlooking." It hearkens back to the Passover in Exodus when the death angel passed over the home with the sacrificial blood of the lamb on the doorposts. God passes over those with faith in the blood of Christ.