"5Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be a peculiar treasure unto me above all people: for all the earth is mine: 6And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel." (Exodus 19: 5-6)
Under law, the Israelites were required to keep their part in God's Covenant, every single jot and tittle.
Of course, because no one can keep God's law, He lovingly provided an altar of sacrifice, so that they could still come to Him, in spite of their sin:
"24An altar of earth thou shalt make unto me, and shalt sacrifice thereon thy burnt offerings, and thy peace offerings, thy sheep, and thine oxen: in all places where I record my name I will come unto thee, and I will bless thee. 25And if thou wilt make me an altar of stone, thou shalt not build it of hewn stone: for if thou lift up thy tool upon it, thou hast polluted it." (Exodus 20: 24-25)
Today, because of the perfect sacrifice of Jesus, we are brought into a royal priesthood:
"9But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light: 10Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy." (1 Peter 2: 9-10)
Peter explains why we are a royal priesthood today:
"3Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead, 4To an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you" (1 Peter 1: 3-4)
Notice that under law, God invited the Israelites to become a "kingdom of priests". Under grace, we are a royal priesthood. Not only is Christ our King, but today we reign in life with Him:
"For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ." (Romans 5: 17)
"If we suffer, we shall also reign with him: if we deny him, he also will deny us:" "(2 Timothy 2: 12)
Today, we are more than priests, but kings and priests in Christ Jesus!