Heaven is the ending of the Throne of Glass series. (So if you haven't read it but want to, or if you are reading it currently and haven't finished yet, be advised. I worked very hard to avoid any sort of spoilers, but if you are already reading the series I would say just wait until you finish it.)
The ending of Kingdom of Ash just made me think of what getting to heaven will be like. A massive battle that encompasses the entire world (actually even more than one world) is the big climax that we have been leading up to for six books before this. Six thick, very substantial books. It has always been leading up to this from the very, very beginning, but the very, very beginning was now a long time ago. The battle is colossal, and some things happen that you just knew were gonna happen all along, and some things catch you totally by surprise. You lose people you didn't expect to along the way, and the grief and pain shatter your heart. And you gain people along the way and it warms the broken pieces of your heart. Things you knew had to happen do happen, but not at all in the way you were expecting. But as you had hoped (and kinda knew would happen) the world is saved, in magnificently epic fashion no less. And then you can finally breathe and look around. And you see the devastation, and it is total, but you know that you get to leave it all behind now. And as you move forward into the final happy ending, you are grieved by those who didn't make it with you, and you wish with all your heart that they could be here with you and see the end of it all and live the happy ending with you. But they can't, so then you move on, and the happy ending is SO HAPPY you can hardly believe it and it just completely overwhelms you. It is everything you wanted and waited and hoped and prayed for. Things you didn't even know to hope for in the very beginning when things were so much simpler but that took root along the way, and the things you knew from the first chapter that you wanted to see by the end, it all comes together for the most glorious ending. And this is why it is so glorious: because it's not really an ending, but a new beginning in absolute joy.