Pentecost isn't important because we aren't told to celebrate it in the New Testament, therefore we can't celebrate it.
Uh, that is the same logic that says the fourth Commandment is no longer in effect. You believe that? The following is a C&P...
God's Festivals in the New Testament
The New Testament records Jesus Christ, the Apostles and the Church keeping the Holy Days.
1. Passover
Commanded in Old Testament:
Leviticus:23:5
Observed by Jesus Christ, the apostles or the Church in the New Testament:
Matthew:26:2, 17-19
Mark:14:12-16
Luke:2:41-42
; 22:1, 7-20
John:2:13, 23; 6:4; 13:1-30
1 Corinthians:11:23-29
2. Feast of Unleavened Bread
Commanded in Old Testament:
Leviticus:23:6-8
Observed by Jesus Christ, the apostles or the Church in the New Testament:
Matthew:26:17
Mark:14:12
Luke:2:41-42
, 22:1,7
Acts:20:6
1 Corinthians:5:6-8
3. Feast of Pentecost
Commanded in Old Testament:
Leviticus:23:15-22
Observed by Jesus Christ, the apostles or the Church in the New Testament:
Acts:2:1-21
; 20:16
1 Corinthians:16:8
4. Feast of Trumpets*
Commanded in Old Testament:
Leviticus:23:23-25
Observed by Jesus Christ, the apostles or the Church in the New Testament:
Matthew:24:30-31
1 Thessalonians:4:16-17
Revelation:11:15
5. Day of Atonement
Commanded in Old Testament:
Leviticus:23:26-32
Observed by Jesus Christ, the apostles or the Church in the New Testament:
Acts:27:9
6. Feast of Tabernacles
Commanded in Old Testament:
Leviticus:23:33-43
Observed by Jesus Christ, the apostles or the Church in the New Testament:
John:7:1-2
, 8, 10, 14
7. The Eighth Day (sometimes called the Last Great Day)
Commanded in Old Testament:
Leviticus:23:36
Observed by Jesus Christ, the apostles or the Church in the New Testament:
John chapters 7-9
*Although the Feast of Trumpets is not mentioned by name in the New Testament, the theme of the day—the sounding of trumpets announcing Jesus Christ's return—is mentioned by several New Testament authors as noted in the references.
From the sight...
God's Festivals in the New Testament | United Church of God