פּירוש אויף דברים 12:28

שמר KEEP [AND HEAR (understand) ALL THESE WORDS WHICH I COMMAND THEE] — This (the word שמר) implies the studying of the oral law — that you must keep it within you that it should not be forgotten, just as it is said, (Proverbs 22:18) “[And apply thy heart unto my knowledge] for it is a pleasant thing if thou keep (תשמרם) them within thee”, and only if thou learnest is it possible that thou wilt understand and fulfil the commands, but one who is not amongst those who study (lit., who is not included in learning) cannot be amongst those who act correctly (cf. Sifrei Devarim 79:3; see also Rashi on Deuteronomy 4:6). (The translation is: keep, i.e. study and retain your learning in mind: ושמעת, and then thou wilt understand how to observe the commands).

OBSERVE AND HEAR ALL THOSE WORDS WHICH I COMMAND THEE. He [Moses] did not mention here the statutes and ordinances, nor His testimonies and His commandments, but said all those words in order to include in this observance the good and the right, as I have explained in the section of Va’ethchanan.⁹²Above, 6:18.

observe and heed to spill the blood at the side of the Altar.

את כל הדברים [KEEP …] ALL WORDS [WHICH I COMMAND THEE] — This implies that a light precept should be as dear to you as a grave precept (Sifrei Devarim 79:4).