The law came through Moses. Moses was a Levitical priest. Therefore, the law came through the Levitical priesthood.
Lev 26:46 These are the statutes and judgments and laws, which the LORD made between him and the children of Israel in mount Sinai by the hand of Moses.
Num 31:21 And Eleazar the priest said unto the men of war which went to the battle, This is the ordinance of the law which the LORD commanded Moses;
Deu 4:44 And this is the law which Moses set before the children of Israel:
Jos 22:5 But take diligent heed to do the commandment and the law, which Moses the servant of the LORD charged you, to love the LORD your God, and to walk in all his ways, and to keep his commandments, and to cleave unto him, and to serve him with all your heart and with all your soul.
Moses was in the business of transcribing God's dictation. Moses was in the business of hearing God because the people feared God when they heard Him speak and asked of God that only Moses hear His voice. Moses did not speak his own words. Jesus did not speak His own words.
Exo 19:5 Now 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:
Exo 19:6 And 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.
Exo 19:7 And Moses came and called for the elders of the people, and laid before their faces all these words which the LORD commanded him.
Psa 12:6 The words of the LORD are pure words: as silver tried in a furnace of earth, purified seven times.
Psa 119:57 CHETH. Thou art my portion, O LORD: I have said that I would keep thy words.
Isa 58:13 If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day; and call the sabbath a delight, the holy of the LORD, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
Isa 59:20 And the Redeemer shall come to Zion, and unto them that turn from transgression (rebellion/disobedience) in Jacob, saith the LORD.
Isa 59:21 As for me, this is my covenant with them, saith the LORD; My spirit that is upon thee, and my words which I have put in thy mouth, shall not depart out of thy mouth, nor out of the mouth of thy seed, nor out of the mouth of thy seed's seed, saith the LORD, from henceforth and for ever.