Exode 19:5

"And now" - If you accept it upon yourselves now, it will become pleasing to you [beginning] from here and in the future, since all beginnings are difficult. (Mekhilta; Bavli Shabbat 87a)

"And if you keep my covenant" - Which I will make with you about keeping the Torah.

"Treasure" - A beloved trove like "the treasure of Kings" (Ecclesiastes 2:8), a precious vessel with beautiful stones where the king stores them. Thus, you should be for me a treasure from the other nations. You should not say that you alone are mine and I do not have any others with you. I do this all the more so my love of you is known since all of the earth is mine and they [Israel] are in my eyes and before me more than anything else.

And now, if you will truly hearken to My Word and keep My covenant, you shall be more beloved before Me than all the peoples on the face of the earth.

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.” 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.
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,, 23:22.

then ye shalt be Mine own ‘s’gulah’ (treasure) from among all peoples.” This means that “you will be a treasure ‘in My hand,’” for a king does not hand over a precious object into the hand of another [for permanent possession]. The word s’gulah here is similar in meaning to the expression: ‘us’gulath’ (and treasure) such as kings and the provinces have as their own.
FOR ALL THE EARTH IS MINE. This is similar in meaning to the verses: Which the Eternal thy G-d hath allotted unto all the peoples… But you hath the Eternal taken. And thus He said, “And I have set you apart from the peoples, that ye should be Mine [own] treasure.” It may be that the word s’gulah connotes “attachment.” [The sense of the verse would then be: “and you shall be attached to Me from among all peoples], for unto Me is the earth called kol (all),” as I have explained on the verse, And the Eternal had blessed Abraham ‘bakol’ (in all things). The student learned [in the mystic lore of the Cabala] will understand. Similarly, And ye shall be unto me means that “you will be Mine in a special sense, and not as the rest of the peoples.” And so did the Rabbis interpret it in the Mechilta: “And ye shall be unto Me. As though it were possible to say it, [He is stating], ‘I shall neither appoint nor delegate [any power] to rule over you, but I Myself will rule over you.’ And thus it says, Behold He that keepeth Israel doth neither slumber nor sleep.”

כי לי כל הארץ, all the nations are Mine, but I have only chosen you.

And you will be a treasure among all peoples - even though all types of humans are important to me above all the lower beings, since He is represented only in them, as say Hazal (Avot): 'Humans are beloved because they were created in the Image' - still, you will be treasured among them

...Because Mine is all the earth - and the difference between you exists in smaller or bigger amounts, despite the fact that the whole earth is Mine, and the Righteous of the Nations are important to Me without a doubt.