Kira Nerys has been intensely religious for as long as she can remember.
Of course, she wouldn't put it like that - intense sounds negative, like you're saying someone can be overly religious, too religious. And she doesn't believe that. She respects that other people experience religion differently from her, or not at all, and she would never try to tell them that they're wrong to do so. Likewise, neither is the way she does things: praying daily, asking for heavenly advice on routine matters, obeying what some would call outdated superstitions because her church as a child obeyed them, and even if her beliefs have shifted as she's moved from church to church, the oldest lessons stay with you longest.
She loves what she does - working in the government can be a frustrating position, but it has countless rewards as well. As mayor, she gets to work with so many different wonderful people in the community: Odo, the police chief; Opaka Sulan, the minister of the church the next county over most of the town's residents go to; Keiko O'Brien, the young new principal of the town's public school. Quark, head of the town's merchants association, is more of a frustration than a reward, but even he brings some... interesting insights. And working with all these people, she gets to do things that clearly and visibly help others in her community. She knows she does good work.
She knows she does good work, and she loves doing it... but still, she feels like it isn't enough. Like she's waiting for a higher power to reach out and tap her on the shoulder and say, "Here's that higher calling you were looking for."
So when that literally happens one day - when angels speak to her with voices so beautiful she wants to cry, and they tell her they have need of her - she jumps at the chance. When they say they need to borrow her body, she doesn't question that. She consents, readily, eagerly. The angel that possesses her fills her up with light so bright it nearly hurts, and it makes her feel small and humble in ways she never has before, but she's glad to do it. No matter how much it takes out of her, no matter how long they need her.
So she thinks.