What is the meaning of "Al Yalizu me'Einecha"?
R. Yonah: This warns to always put the Mitzvos on his heart and in front of his eyes, lest he be negligent about fulfilling them 1 . There are two ways of forgetting - forgetting the Ikar (primary matter), and forgetting the occasion. The former is like forgetting the Mitzvah or warning. One who forgot the Ikar of Shabbos, and did many Melachos on many Shabbosos, is liable only one Chatas (Shabbos 67b). Forgetting the occasion is one who knows the Mitzvah or warning, but temporarily forgot it and transgressed it. E.g. he knows that one must don Tefilin, affix a Mezuzah, recite Keri'as Shma and pray, but did not think about them and did not fulfill them. Or, he knew that Chadash is forbidden, and passed by a grain field, and did not think about the Isur and ate Chadash. He was Poshe'a, for he hid memory of the warning from his eyes. However, if he saw detached Chadash grain, and thought that it is Yashan, this is Shogeg. The Peshi'ah of forgetting the occasion is greater than that of forgetting the Ikar, for [the former] knows the Mitzvah, but is not mindful to fulfill it.
Malbim: In all your acts, Divrei Torah should be in front of your eyes to act according to its Mitzvos.
R. Yonah: Also above (3:21) it says "Al Yaluzu me'Einecha." Perhaps here it says Yalizu (Hif'il), that affairs and distractions should not remove them from his eyes.
What is the significance of "Shamrem b'Soch Levavecha"?
R. Yonah: This warns against forgetting the Ikar 1 . He should think about the Mitzvos constantly, lest he forget any of them. The Torah warned about this - "Hishamer Lecha u'Shmor Nafshecha Me'od Pen Tishkach Es ha'Devarim... u'Fen Yasuru mi'Lvavecha" (Devarim 4:9). One who forgets a matter of learning transgresses three Lavim, for Hishamer, Pen and Al are Lavim (Menachos 99b). "Motza Sefasecha Tishmor v'Asisa" (Devarim 23:24) warns against Peshi'ah of forgetting the Ikar of a Neder. One who does not fulfill it in time transgresses Bal Te'acher. From when he vowed, he must be mindful not to forget, for he knows that forgetting is common if one does not guard the matter in his heart. "Al Titen Es Picha Lachati Es Besarecha" (Koheles 5:5) - Even if in the end you are Shogeg about transgressing the Neder, it will not be considered Shogeg, for you did not put it to heart to not forget it.
Malbim: Guard Divrei Torah in your heart to think about them constantly, according to the ways of Chachmah.
R. Yonah: The counsel to avoid forgetting the Ikar is to constantly learn Torah and to grow up among Chachamim. The counsel to avoid forgetting the occasion is to write the 613 Mitzvos, and look at them once or twice a week, and put to heart if he fulfills all of them. If he sees that he did not, he should repent, confess and be more careful. If he sees that he fulfilled them, he should thank Hashem and rejoice in his heart. Simchah in the heart is an Ikar of Avodah. So David did - "Achalai Yikonu Derachai...; Az Lo Evosh" (Tehilim 119:5-6).
