''He trusted in Hashem, and He considered this for him as an act of righteousness'' [Lech Lecha 15:6]
Why, asked the Chofetz Chaim, was Avraham's trust in Hashem considered 'righteousness' - as though it was something above and beyond what was demanded of him? After, all, Avraham fulfilled every commandment in the Torah; what was so unique about his trust in Hashem?
We see from here, answered the Chofetz Chaim, that trust in Hashem is more than just another mitzvah, rather it is the foundation of the entire Torah.
To what can this be compared? To a man drowning in the sea who suddenly sees a tree extending from the shore. Which part of the tree will he attempt to grab? Not the branches, for they can easily be broken off; rather, he grabs hold of the roots.
So too, concluded the Chofetz Chaim, is trust in Hashem. Trust in Hashem is comparable to the sturdy roots of a tree, which serve as a foundation and a base for the entire tree.
Source: Rabbi Yisrael Bronstein