Reading from Exodus Chapters 16, 20 and 31 LXX Brenton.
The Sabbath was first explained by Moses to the people of Israel at the beginning of their wandering in the wilderness of Sinai, when they were gathering manna in Exodus 16:23 - 30. It was then given to Moses as fourth of the Ten Commandments in Exodus 20: 8 - 11.
Later, in Exodus chapter 31, a stern final reminder was given to Moses, before God gave him the two tables of testimony, engraved by the finger of God, that His people must keep the holy Sabbath. This reminder is accompanied by a warning that anyone who does work on the Sabbath "that soul shall be destroyed from the midst of his people" (Exodus 31:14), and a reiteration that it is a perpetual covenant between God and the children of Israel (Exodus 31:17).
Having received such a stern reminder from God, Moses went on to remind the children of Israel about taking pains to keep the Sabbath, in Exodus 35:1,2, before making announcements to them on taking offerings of raw materials for the construction of the Tabernacle and for the vestment of Aaron the High Priest.
Exodus 16:23 - 30 LXX
23 And Moses said to them, Is not this the word which the Lord spoke? To-morrow is the sabbath, a holy rest to the Lord: bake that ye will bake, and seethe that ye will seethe, and all that is over leave to be laid by for the morrow.
24 And they left of it till the morning, as Moses commanded them; and it stank not, neither was there a worm in it.
25 And Moses said, Eat that to-day, for to-day is a sabbath to the Lord: it shall not be found in the plain.
26 Six days ye shall gather it, and on the seventh day is a sabbath, for there shall be none on that day.
27 And it came to pass on the seventh day that some of the people went forth to gather, and found none.
28 And the Lord said to Moses, How long are ye unwilling to hearken to my commands and my law?
29 See, for the Lord has given you this day as the sabbath, therefore he has given you on the sixth day the bread of two days: ye shall sit each of you in your houses; let no one go forth from his place on the seventh day.
30 And the people kept sabbath on the seventh day.
Exodus 20:8 - 11 LXX
8 Remember the sabbath day to keep it holy.
9 Six days thou shalt labour, and shalt perform all thy work.
10 But on the seventh day is the sabbath of the Lord thy God; on it thou shalt do no work, thou, nor thy son, nor thy daughter, thy servant nor thy maidservant, thine ox nor thine ass, nor any cattle of thine, nor the stranger that sojourns with thee.
11 For in six days the Lord made the heaven and the earth, and the sea and all things in them, and rested on the seventh day; therefore the Lord blessed the seventh day, and hallowed it.
Exodus 31:12 - 18 LXX
12 And the Lord spoke to Moses, saying,
13 Do thou also charge the children of Israel, saying, Take heed and keep my sabbaths; for they are a sign with me and among you throughout your generations, that ye may know that I am the Lord that sanctifies you.
14 And ye shall keep the sabbaths, because this is holy to the Lord for you; he that profanes it shall surely be put to death: every one who shall do a work on it, that soul shall be destroyed from the midst of his people.
15 Six days thou shalt do works, but the seventh day is the sabbath, a holy rest to the Lord; every one who shall do a work on the seventh day shall be put to death.
16 And the children of Israel shall keep the sabbaths, to observe them throughout their generations. 17 It is a perpetual covenant with me and the children of Israel, it is a perpetual sign with me; for in six days the Lord made the heaven and the earth, and on the seventh day he ceased, and rested.
18 And he gave to Moses when he left off speaking to him in mount Sina the two tables of testimony, tables of stone written upon with the finger of God.
Exodus 35:1, 2 LXX
And Moses gathered all the congregation of the children of Israel together, and said, These are the words which the Lord has spoken for you to do them.
2 Six days shalt thou perform works, but on the seventh day shall be rest—a holy sabbath—a rest for the Lord: every one that does work on it, let him die. 3 Ye shall not burn a fire in any of your dwellings on the sabbath-day; I am the Lord.