# food sacrificed to idols
Gentile worshipers would offer grain, fish, fowl, or meat to their gods. The priest would burn a portion of it on the altar. Paul is speaking of the portion the priest would give back for the worshiper to eat or sell in the market.
# Knowledge puffs up
"Knowledge makes people proud" or "People who think that they know a lot become proud"
# but love builds up
"but when we love people, we build them up"
# love builds up
"love strengthens people" or "when we love people, we strengthen them"