Frankly, it sounds like gobbledegook to me. It might make more sense if I knew the context, particularly the next few sentence. "Is a function of" means "is determined by" or "is caused by."
"All behavior is a function of its consequences" actually sounds like a logical impossibility, because the behavior causes the consequences, so how can those consequences be the cause of the behavior?
It is probably shorthand for something like "All behavior is a function of its expected consequences," or "future behavior is shaped by the consequences of past behavior," or "the root cause of all behavior is the consequences that followed past behavior."
It sounds like the writer belongs to "behaviorist" school of human psychology. Behavior is explained by what actions are followed by positive or negative reinforcement.