Why does it say here "Rabos Machashavos b'Lev Ish"?
R. Yonah: This explains the previous verse "Lema'an Techkam b'Acharisech" (refer to 19:20:2:1).
Malbim: Machashavos are what a person thinks - all possible ways to reach a goal. They are many, and they are in one's heart. He has choice to choose one of them. Etzah is the proper counsel for the desired goal.
Alei Shor 2 p. 252: Obviously, Hashem's counsel will be done! The Chidush is, a person should toil with many thoughts to resolve a matter, and try to find what is "Atzas Hashem." It is already found in man's heart; he must strive to distinguish between the many thoughts and Hashem's counsel. Just like a hair's breadth can distinguish between Tahor and Tamei, also here!
What is "Atzas Hashem"?
Sanhedrin 26b: It is Torah. If one learns Lishmah, planning (or worry) will not harm 1 his Torah - "Rabos Machashavos b'Lev Ish va'Atzas Hashem Hi Sakum."
R. Yonah: This is like "Ki Hashem Tzevakos Ya'atz u'Mi Yafer" (Yeshayah 14:27); He decreed and said.
Malbim: It is his decision and desire. Even though man has choice, the final act is under Hashgachah. Hashem's Etzah will stand and nullify choice.
26b: Planning (or worry) inhibits one from fulfilling his goal, even Torah - "Mefer Machshevos Arumim v'Lo Sa'asenah Yedeihem Tushiyah."
