2 Corinthians 3:6 who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
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)
Shavuot, or the Feast of Weeks, is celebrated fifty days from the feast of first fruits. The number 50 recalls the Jubilee cycle described in the book of Leviticus; a number which is associated with liberty, freedom, and deliverance since each jubilee cycle required that slaves and captives be set free and every debt canceled. As such, the number 50 and its significance as a "Jubilee" speaks to us of freedom, deliverance, and salvation from our spiritual debt and the bondage of sin. The first "Pentecost" emphatically revealed this significance with 3000 saved souls.
So for us as believers, Shavuot / Pentecost recalls, on the one hand, our freedom from the power of sin, which is the law [1 Cor. 15:56], our canceled debt, our deliverance from the slavery of the old nature; and on the other, reminds us of the source of our life and the power of our witness and service, the Holy Spirit: "not in the oldness of the letter, but in the newness of the Spirit."
Remember, you have been freed from the bondage of sin and dead works, and cannot please the Lord apart from His own empowering of your life and service. His Holy Spirit was given because apart from Him we can do nothing. Shavuot ought to be a powerful reminder of this amazing reality.