From a neutral, Bible-based perspective.
The fact that the Father, Jesus and the Holy Spirit are still offended at sins is visible in verses like the following:
1 John 3:20-22 NIV
If our hearts condemn us, we know that God is greater than our
hearts, and he knows everything...
And what's happenning (from the point of view brought forward in your question) with the removal of world's sin once for all time through the sacirifce two millenia ago, can be summarized as follows.
Since the verses about the removal of world's are in the Bible, it is truth, no need to explain why. Now, lets hypothesize for a moment that truth is a quantum concept. To try to prove it, lets consider how an electron is a quantum particle, which goes through truth/false gates as it travels. Light is also a quantum concept, and Christ compares himself to light. And most importantly, the Bible speaks of how we must believe the truth, for it to start to work in our lives, see John 1:12. How does this particular verse helps the entertained hypothesis? It helps it because in quantum mechanics there is an observer, whose presence changes quantum object from being non-tangible (wave) into being tangible (particle), tangible here referring to that "activeness" the truth starts to have on those who received it. These things give the hypothesis significant strength.
And so it is quite fair to say that though it is true that Christ had already atoned for everyone's sin, yet those that seek salvation must still receive that truth first, by believing in it, by becoming observers/witnesses to it.
This outlook also explains how someone already a Christian can commit something evil and fall into an at least temporary disfavor with God like in 1 Corinthians 5:4-5 NIV:
So when you are assembled and I am with you in spirit, and the power
of our Lord Jesus is present, 5 hand this man over to Satan for the
destruction of the flesh, so that his spirit may be saved on the day
of the Lord.
To elaborate and clarify, it should be said that since truth is either inside or outside of us, our sin can simply cast it out from within ourselves, and we would need to try to recieve the truth again, once we mend the holes it created, so that truth doesn't spill out from us again like wine from a broken bottle. To clarify, sin is really just guilt:
Romans 14:14 NIV
I am convinced, being fully persuaded in the Lord Jesus, that nothing
is unclean in itself...
Leviticus 5:2-3 Brenton Septuagint
That soul which shall touch any unclean thing, or carcase, or that
which is unclean being taken of beasts, or the dead bodies of
abominable reptiles which are unclean, or carcases of unclean cattle,
or should touch the uncleanness of a man, or whatever kind, which he
may touch and be defiled by, and it should have escaped him, but
afterwards he should know, —then he shall have transgressed.
To further elaborate on the nature of guilt, since it is directly important in understanding the interplay between truth and sin, it should be noted that if we don't deal with it quickly enough, it can harm our salvation and areas of life under God's blessing, according to the symbolism of different places in the Bible. For example, guilt, like hot coals, burns a hole in our wineskin and causes the wine (the Holy Spirit / the truth) to flow out. The connection between the wineskin parable and the hot coals may seem far-fetched, yet we do not know what had caused the need for a patch on the wineskin in the first place, and it can be seen how hot coals are portrayed as weapons of spiritual destruction in Psalm 140:10 NIV:
May burning coals fall on them; may they be thrown into the fire, into
miry pits, never to rise.
This delayed action motif is likewise symbolized in how manna would rot if left for too long, which would cause Moses (the symbol for God) to become angry. To elaborate on the latter symbolism, the "manna of guilt" is sometimes given to us by God to help us grow spiritually, to change and improve, but if we neglect it, it can become a problem to us, which is an interpretation that well fits with the Bible and the outlook on truth given here.
