I have heard so often that God spoke only to Israel, didn't mean for the gentiles to listen in at all.
When and where has
anyone suggested that God "didn't mean for the gentiles to listen in at all"? I think you made that up.
Yet my concordance tells me the KJV has 117 verses about the stranger among them and 7 verses about the sojourner. I printed all these verses, and almost every one said that what the Lord told Israel was also for the stranger or the sojourner. To me that tells me that God includes instructions to us all, not just Israel, but others do not see that in these scriptures. I am not understanding why?
You aren't understanding why because you cling to the idea that the Old Covenant was given to all humankind, when plainly, it was given specifically to Israel. The
very few sojourners and strangers who wanted to join with Israel were required to abide by the Law as given to Israel. In the same way, if someone wants to immigrate to the United States, that person must abide by the laws of the United States. However, that person is
not bound by the laws of the United States
prior to emigrating there. The rest of humanity was not given the Law... period.