It is the way of the Blessed Creator to do good
and benefit [His creations], specifically His
nation, Klal Yisrael, who are called the “children
(Devarim 14:1; Avos 3:14). Certainly any father strives to
provide what his child lacks and give him everything
he could wish for, even before the child needs it. And
certainly when a man has faith in the Creator [that He
provides everything he needs], the Creator in turn
provides everything he lacks.
This is what our verse is saying. “You shall have
perfect faith in Hashem", when your at the
level that you believe in Hashem with perfect faith
that He will provide anything you lack, then should know that you are “with Hashem, your G-d" that G-d is with you [and He will provide for you].
[Meoros Tzadikim on the name of Rav Levi Yitzchak of Berditchev]