The nation of Israel received the Law Covenant fifty days after the Passover in Egypt. Thus, historically, Pentecost (meaning 50) was very important. However, Pentecost in the New Testament is even more significant.
At 30 years of age, Jesus became Christ (meaning Anointed) when He was anointed with the holy Spirit at His baptism. Jesus sacrificed His human will to obey and fulfill only God’s will. Hebrews 10:9, “‘Behold, I have come to do Your will, O God.’ He takes away the first (the Law Covenant with its typical sacrifices of bulls and goats) that He may establish the second (the New Covenant).”
Jesus spent His adult life sacrificing His entire being to redeem mankind. Yet, in the Garden of Gethsemane, He agonized over the acceptableness of His life work. Had He in any detail sinned, and thus not become an acceptable ransom for Adam? Jesus had the future of the whole human race on His shoulders. God heard His prayer and sent angels to comfort Him.
From that time forward, Jesus was able to endure, without doubts, the torments and suffering of the cross. On the cross, when Jesus did cry out, He was experiencing the full penalty of sin. Jesus was forsaken by God and treated like a sinner with full alienation from His Father. (It was this complete alienation which actually ruptured His heart from grief.)
Pentecost with the outpouring of the holy Spirit was the outward proof that Jesus’s sacrifice had been fully accepted by the Father. The anointing of the holy Spirit could now come upon believers because Jesus’s sacrifice fully paid Adam’s debt. Thus, the outpouring of the Spirit testified that the ransom had been paid and the heavenly calling of the church had been opened. 2 Timothy 1:10, “Our Savior Jesus Christ, who has abolished death and brought life and immortality to light through the gospel.”