The importance of any holiday in religion is based on what it stands for. The same can be said for Pentecost. Even though not many people celebrate Pentecost, they may be aware of it based on what their church does. They may only celebrate it when they go to church. It also takes a few weeks to celebrate it including 50 days. The importance of Pentecost is based on what it represents.
This was the time when the Holy Spirit met with the followers of Jesus after his crucifixion and resurrection. This shows the miracle of Christianity. Many churches celebrate it by decorating themselves and the churches in red and white colors. They may see sashes on the ministers that are red, white or both.