When the Israelites were held as slaves in Egypt, God commanded Pharaoh, via Moses, to ‘Let my people go’ (Ex. 5:1). You may remember that the Israelites had not yet discovered God’s purpose for them as a people. All they knew was slavery and the desire to be set free.
What they later discovered at Sinai and in the giving of the law, was that they were a nation created by God with a purpose – to be lights to the other nations – so that the whole world will know God and be filled with His glory. Israel was born as a nation on the slopes of Mount Sinai at that first Shavuot (Pentecost) and they were commissioned to be a light to the nations.
Sin and idolatry
Right from the beginning we see the problem of sin and idolatry, and Moses is sent back down the mountain by God to a people worshipping a golden calf. On that first Pentecost, 3,000 Israelites died in God’s judgment of their sin (contrast that with 3,000 Israelites being saved at the first Pentecost after Jesus’ resurrection).