If you want to understand that snippet of a verse well, you’ll need more context than that:
“What advantage is there in being a Jew… are we better off? Not entirely, for we have already brought the charge against Jews and Greeks alike that they are all under the domination of sin. … For there is no distinction; all have sinned.” (Romans 3:1, 9, 22, 23)
You see, brother, that Paul is talking about two groups of people – Jews and Greeks – and in doing so, when referencing both groups, he uses the word “all”. (In v9, “Jews and Greeks alike… are all under the domination of sin.”)
So, when you quote v23, “all have sinned,” Paul means “Jews and Greeks alike have sinned”, not “all persons who have ever lived have sinned.” After all, as @Edwin points out, you wouldn’t say that a child who dies as an infant has sinned… would you? That right there would nullify your case and make the Bible a liar. We can’t hold that to be true!
Therefore, when we see a situation in which the Bible appears to contradict itself, then we must ask where our understanding is in error. Clearly, it’s in your assertion about Romans 3:23, wouldn’t you say?
No, that’s not what Catholics say. When Catholics speak of the “Immaculate Conception”, they’re talking about the conception of Mary in her mother’s womb, and not the conception of Jesus in Mary’s womb. Mary wasn’t “made clean” when she conceived Jesus; rather, she was conceived without sin and remained so throughout her life. Gabriel’s exclamation to her (“chaire, kecharitomene!”) gives witness to the fact that she was saved through grace… but just in a different manner than the way that we are. We’re both saved by grace through faith; hers simply happened when she herself was conceived.
Correct. Mary’s “slate was wiped clean” at her own conception.