¹⁷ At Mount Sinai, Jehovah made a unique national covenant between himself and Israel​—the Law covenant, with Moses as its mediator.b (Galatians 4:24, 25) The people agreed to be in this covenant, and it was validated with the blood of bulls and goats. (Exodus 24:3-8; Hebrews 9:19, 20) It gave Israel theocratic laws and an outline for a righteous government. The covenant forbade intermarrying with pagans or sharing in immoral and false religious practices. It thus guarded the Israelites and was a force in preserving the line of the seed uncontaminated. (Exodus 20:4-6; 34:12-16) But since no imperfect Israelite could keep the Law completely, it made sins manifest. (Galatians 3:19) It also pointed to the need for a perfect, permanent priest and for a sacrifice that would not have to be repeated yearly. The Law was like a tutor that led a child to the needed instructor, who would be the Messiah, or Christ. (Hebrews 7:26-28; 9:9, 16-22; 10:1-4, 11) When it had accomplished its purpose, the Law covenant would end.​—Galatians 3:24, 25; Romans 7:6; see “Questions From Readers,” page 31.

18. What further prospect was involved with the Law covenant, but why was this difficult to understand?

¹⁸ When making this temporary covenant, God also mentioned this thrilling objective: “If you will strictly obey my voice and will indeed keep my covenant, then you will certainly become my special property . . . And you yourselves will become to me a kingdom of priests and a holy nation.” (Exodus 19:5, 6) What a prospect! A nation of king-priests. How could that be, though? As the Law later specified, the ruling tribe (Judah) and the priestly tribe (Levi) were allotted different responsibilities. (Genesis 49:10; Exodus 28:43; Numbers 3:5-13) No man could be both a civil ruler and a priest. Still, God’s words at Exodus 19:5, 6 gave reason to believe that in some undisclosed manner, those in the Law covenant would have opportunity to provide the members of “a kingdom of priests and a holy nation.”