But Jer 31:1 describes “ALL the families of Israel” as being faithful at some point.

In contrast, true atheists are rare in most nations, but common among the Jews. Further, the number of modern Jews who are not really atheists, but who are actually very secular, or even anti-religious in their thinking and outlook, seem to be in the majority among modern Jews. The Jews will on one hand claim to you and me that God was the one who promised Palestine to them, but on the other hand, treat Genesis as a children’s fairy tale if serious discussion of Scripture starts. Still Jeremiah says that,

“At that time, says Yahweh, will I be the God of all the families of Israel, and they shall be my people.”
Jer 31:1 WEB

Over two thousand years have passed and
this has NEVER happened!

Is this a false prophecy?

In truth, this present rejection of God and His Messiah was clearly forecast in many Scriptures, such as Isa 8:14-15. It is even implied in the grand context of Jeremiah himself that this glorious time will come only after much correction and hardship and suffering because of the ongoing sins of the Jews.. We might assume that since so much time has past, that the prophecy is now void. Jesus says something else:

“Scripture Cannot Be Broken,” Jn 10:35 KJV

If you believe the Word of God, then what do you make of Jer 31:1? This means it just has not happened yet! After over 2,000 years? YES! This in fact is dealt with in innumerable Old Testament passages, and several in New Testament, including Roman chapters 9 to 11.

Then look at Time in Jeremiah 31.

See first that the order in which things are discussed is NOT necessarily the order in which things will happen! It is a conversational order of discussion in much of Bible prophecy. Just like in a human conversation, not everything is in sequential time order. God is having a conversation with your and me about the future.

Secondly it should be seen that it is not a human time perspective in Scripture, but an eternal time perspective. That is the real time scale we are on. Remember “that one day is with the Lord as a thousand years, and a thousand years as one day.” 2Pe 3:8 WEB. So an interruption of two thousand years is as nothing in this perspective, as Yahweh works to save as many men as possible. We do not really know how much more there is to come, even though we are clearly told to be watching.

It is as if God said, Yes one day all the families of Israel will be my people. I will send my Son as a baby. Many will be killed in the attempt to kill Him, and He will bring a New Covenant that will write My law on the hearts of My people. In the end it will be well for the Jews.

Clearly it is easy to make naïve assumptions
about time in prophecy!

WEB is the World English Bible, a copyright free revision
of the original ASV American Standard Version 1901