This is probably best handled as a widget, there's no real need to write a whole new macro just for that. Put this in a widget-tagged passage:
<div align="center"><<include $args>></div>
And use it like:
<<includec 'passage name'>>
You should always try to place passage names in quotes when passing them to macros and widgets like <<link>>, <<goto>> and <<include>>; you can wind up confusing the parser if you pass a macro a passage name that has a space or certain other special characters.