Tafsiran Keluaran 19:5: Rashi, Chizkuni, Ramban & Or HaChaim

ועתה AND NOW — if you will now take upon yourselves the observance of My commandments, it will be pleasant (easy) to you from now and henceforth, for every beginning is difficult (Mekhilta).

ושמרתם את בריתי, “you are to observe My covenant;” this refers to the covenant of blood discussed in Exodus 24,8, that Moses took the blood of the different types of offerings presented on the altar he had built and divided it in half, as a sign of a covenant between G-d and Israel.

AND YE WILL KEEP MY COVENANT. I.e., “the covenant which I have made with your fathers to be a G-d unto them and to their seed after them.”¹⁵³Genesis 17:7. Rabbi Abraham ibn Ezra explained it as referring to the covenant which Moses was to make with Israel after the Giving of the Torah, as he said, Behold, the blood of the covenant, which the Eternal hath made with you in agreement with all these words.¹⁵⁴Further, 24:8.
By way of the Truth, [that is, the mystic lore of the Cabala, the verse is to be understood as meaning] that “you should keep My covenant to cleave unto Me, for if thou shalt indeed hearken unto My voice and do all that I speak,¹⁵⁵See Ibid., 23:22.

ושמרתם את בריתי AND KEEP MY COVENANT which I shall make with you regarding the observance of the Torah (cf. (Mekhilta).