When the Torah was given on Shavuot in the days of Moses, the sin of the golden calf resulted in the death of 3,000 men. Some 1500 years later at the same season the Holy Spirit descended causing 3,000 men to be saved! The Lord has never changed; His mercy and His holiness are the same throughout all ages. But the contrast of these two historical events during the same Holy Day may be seen as a powerful illustration of this principle: “the letter [of the Law] kills, but the Spirit gives life." (2 Corinthians 3:6)