Why do mantras have to be prepared?

[BBMouse.6510]

The spirit weapon is kind of like the mantras without preparation stage. It's just a play style. I feel Firebrand elite is more of a group play in dungeons/fractal/raid than solo pve, which preparation is a hassle 'cause you switch zooms frequently and might forget to prepare. Try the spirit weapon if you don't like to prepare. I forgot to prepare all the time and that's why mantras is not my style. But I believe others can do it better. I remember some runes effect could trigger when you prepare for mantras, but I don't know if they are still good nowadays.