I have been doing some research on the question of vayechal at mincha and have hit a roadblock. So far, here are the questions I have considered and feel ok with as "answered": why lain at mincha on ...
Why don't we say Uvah Letzion on Shabbos by Shacharis and say it by Mincha? Moreover, we then commence to repeat it by Maariv. Why do we do that?