What is Pentecost? Pentecost is when the Holy Spirt descended on Jesus’s apostles while they praying together. This filling with the Holy Spirt gave them the powers and abilities they would need to continue Jesus’s work now that he ascended to heaven. Pentecost is hard to picture. How do you describe what the Holy Spirt looks like? The book of Acts in the Bible tells of the many things the apostles did to continue Jesus’s work.