Marcillus will have a more difficult time. The Lightbringer has no power in this land, and limited communication abilities. That leaves three options:
- Use the spells of the Lightbringer with a chance of failure
- Find a god in this plane who will grant spells.
- Research new spells at the Loremaster
A distant fourth option is to kill a god and gain his knowledge, but this is no easy task. Unless fifth level cleric spells are granted by a god of this realm, they will all require a material component. Finding them at a loremaster will require a hard search and 200 gp worth of materials to transcribe and learn.