What is the Teshuva about? Secular Jews, what are they supposed to do? It is not like any threat could make them believe in the historicity of the Torah. For instance, nothing will ever convince them that the Mabul really happened. It will take Moshiach to reconcile the heresy of Sasson, the secular Jew, with the heresy of Simcha, the frum Jew who believes everything.
The collective Teshuva that is required of both Sasson and Simcha is that of the previous post. They have to stand up to the world and declare that the Land is ours, and ours alone.
