In the finale of the TV series Lost, there were many unanswered questions, including why Ben Linus did not enter the church. Ben was a complex character, starting as a villain but redeeming himself over time. However, despite his growth, he chose to stay outside the church while the others entered.
Actor Michael Emerson, who portrayed Ben, believed that his character was waiting for someone specific. Ben was always separate from the main characters of Lost, and Emerson pointed out that every other character entered the church in pairs, except for Ben. It is unclear who Ben was waiting for, but it suggests that there was someone important to him that had not arrived.
Another reason for Ben's refusal to enter the church might be his unfinished business with his "daughter" Alex. In the flash sideways, which was a form of wish fulfillment for the characters, Ben was a history professor who had a strong bond with Alex and her mother Danielle. Outside the church, Ben needed to reconnect with them before they could move on.
Overall, the reason why Ben did not enter the church in the end of Lost remains open to interpretation. But it is clear that he still had personal matters to resolve before he could truly find peace.