What do we learn from "b'Chol Derachecha Da'ehu"?
R. Yonah #1 citing Brachos 63a: This is a small Parashah that all Ikarim of Torah depend on it. Know Him even in an Aveirah! People say that a thief calls to Hashem at the opening of the tunnel. R. Yonah - it is clear from above and below that the verse refers to Bitachon 1 . Ikarim of Torah depend on it. (a) in every facet of every action that you want to do, remember Hashem, and hope to him to make you succeed. Put your trust in Him, and return your heart to Him, for the action is not in your hand. The verse adds to "Betach El Hashem b'Chol Libecha" (5), for some trust in Hashem in general, and believe that all is from Shamayim, and trust in Him and not in man (refer to 21:1:1:3) and not in his own strength and Sechel, but he does not put to his heart trust about particular matters, i.e. every action that he does 2 . Realize that you do not have the ability to do that action. It is in Hashem's hand. Put your hope to His Chesed. So David said "Kivisi Hashem Kivesah Nafshi", "Nafshi la'Shem" (Tehilim 130:5-6). Via being accustomed to this, the Nefesh that desires will come to Bitachon. (b) Both in optional tasks and tasks of Mitzvah. Intent helps even for Divrei Torah (Sanhedrin 26b).
R. Yonah #2: All your actions should be l'Shem Shamayim. Do not seek from this world pleasure, honor and wealth and all desires, only Avodas Hashem.
R. Yonah #3: Amidst distraction in your work, do not forget the yoke of Shamayim, Yir'as Hashem and His grandeur.
R. Yonah #4: At the beginning of every deed, put to your heart if there is sin in that deed, and do not do it until it is clear to you that Hashem desires it. Then, you will succeed, and "He will straighten your ways."
R. Yonah: After warning about Chesed v'Emes, it warns about Bitachon and trusting in Him in all one's ways. We find like this "Chesed u'Mishpat Shmor v'Kave El Elokecha Tamid" (Hoshe'a 12:7).
R. Yonah: Some trust in Hashem for big matters, e.g. to go overseas on business or in a caravan, but not for small matters. It is light in their eyes, and it is clear to them that they will succeed, or there will be a small loss if they do not succeed. Rather, trust in Him in all your ways - big or small. Since all actions depend on Him, and all success is via His Chesed, one must remember Him in all his deeds. If he succeeds and did not lift his eyes to Hashem, he diminished his Avodah. Also, he should put to his heart that the reward for trust and hope in Hashem for the act to succeed, is greater than the benefit of the act itself.
How will He straighten your ways?
R. Yonah #1: Aside from the reward for trust and hope in Hashem, you will succeed in the act of remembering Hashem, and that the action is not in your Reshus.
R. Yonah #2: Aside from the great reward for this Midah (of Bitachon), the action will succeed, for you do it l'Shem Shamayim.
R. Yonah #3: If you will always recall the yoke of Shamayim, Yir'as Hashem and His grandeur, He will make your work succeed - because they are Chasidim, their Torah endures and their work is blessed.
Mesilas Yesharim (Perek 16): After conduct with Perishus (taking from the world only what is essential), one needs to purify his heart and thoughts. Also the little that he takes, he should not intend for pleasure and desire, rather, from the good that comes from that act, based on Chachmah and Avodah.
Malbim: Derech is a great path. Orchos are small paths that branch off from the Derech. The Orchos of Chachmah are countless, for Chachmah spreads over all details which are very numerous. One cannot know all the details, how to conduct in them according to Torah and Chachmah. If you will know Hashem in your general Derachim, e.g. mercy, generosity and humility, go in it according to Hashem's command. Everything depends on "va'Halachta bi'Drachav" (Devarim 28:9) - just like He is merciful