Pentecost as New Sinai

Pentecost Sunday for Christians is the day Christians memorialize the coming of the Holy Spirit. Pentecost is a high voltage New Testament junction box of symbolic connections but one of them I've never explored is how it is New Sinai. The law was meant to form the people of God in the desert. The gift of the Holy Spirit is to shape the people of God in the last days as prophesied by the prophet Joel.