To filter a Smart List by section use the advanced filter at the very bottom of the list.
Then select "matches" and type in the section name with the exclamation mark in front:
!section
If your section uses spaces put double-quotes around it like so:
!"Most important"
Stacking filters
Just like other filters this will get added as another condition that has to be fulfilled.
For example you can also set the filter for "scheduled today" in addition to this advanced filter and get everything from this section that is scheduled today.