I don't understand it, but accept that it is so. But it doesn't necessarily say they were faithfully keeping all the Law. We have now seen decades of God's working to bring Israel back. So, it should be obvious that God is not finished with her yet. Israel rejected Christ.
Branches grow from a main tree, which in turn grows out of a root.
Israel was not bearing fruit, and was pruned from the Vine, Jesus Christ. Ever since their 'birth' in the wilderness, Israel was branched off of Christ. In relegating Israel to the garbage heap, they set themselves up in pride. But Israel's breaking off was for a purpose. Even though they have been at enmity against the Gospel, rejecting Christ, God is going to perform a work in them.