# 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"