Why did crusaders think that they would be sure of a place in heaven?

Crusaders believed that by fighting in the Holy Land to reclaim it from non-Christians, they were fulfilling a divine mission and demonstrating their faith and devotion to God. They saw their participation in the Crusades as a way to atone for their sins and earn salvation by serving a holy cause. Additionally, the Church promised indulgences and spiritual rewards to those who took part in the Crusades, further reinforcing the idea that they would secure a place in heaven.