Our first reading today is the giving of the ten commandments. The time is three months after the Israelites left on their exodus from Egypt. During this three months they have come to a place called Marah (the name means “bitter”) which had bitter water; the people grumbled against Moses, then God has Moses cast a piece of wood into the water and it becomes sweet.
From there they go into the Desert of Sin where the whole community grumbled against Moses and Aaron because they are hungry; then Moses and Aaron tell the people of the food which will be provided and God gives them manna and quail (Numbers 11 tells us that the quail poisoned those who continued to grumble).
Next, they went to Rephidim where the people quarreled with Moses because there was no water. Moses says to them “Why do you quarrel with me? Why do you put the Lord to the Test?;” and God tells Moses to strike the rock at Horeb (Sinai) with his staff and water flows.
Then they are attacked by the Amalekites and defeat them (they win as long as Moses’ hands are up, so Aaron and Hur hold his hands up). After the battle Jethro [Moses’ father-in-law and a priest of Midian (an Arabian nomadic tribe)] visits and convinces Moses to appoint representatives among the people so that every time there is a dispute, Moses doesn’t have to personally resolve it.
Now, they have entered the Desert of Sinai and are camped at the base of Mount Sinai. To best understand the context of today’s first reading, we will begin reading at Exodus 19:3 and continue through the prescribed reading.
You can also use this guide by Fr. Cielo Almazan