Good person that doesn't believe in God?

[Charlemagne_III]

Why can’t someone who is an atheist but who does good deeds every day reach heaven?

Here’s the problem. We all do good deeds every day. But we all also do bad deeds every day.

The bad deeds need to be redeemed. They are probably not redeemed by the good deeds. If they were, we would not need repentance. But since the Church teaches we must all repent of our sins, that applies to atheists as well as to Christians. Atheism is a sin, as the Catechism teaches. So while an atheist can repent if he chooses to repent of atheism, should he choose to die unrepentant, he will die like any Christian who is unrepentant of his sins, and he will be judged accordingly. Or so it would seem unless I stand corrected.

2125 Since it rejects or denies the existence of God, atheism is a sin against the virtue of religion. Catechism of the Catholic Church

There is hardly any other sin that says so blatantly, “I want nothing to do with God.”