“who.” The Hebrew can read “who is before you” (ASV; CJB; DBY; ERV; NAB) or “what it before you” (HCSB; ESV; KJV; NASB; NET; NIV). The native Hebrew reader would instantly see both readings, and the English text could be conflated to read, “carefully discern who and what are before you.” Roland Murphy (Word Biblical Commentary) says that the author may have indeed meant both “who” and “what.” The Young’s Literal Translation may be doing a good job of taking in the whole picture by saying, “that which is before you.” We went with “who” because we felt that the person was more important than the food.
This verse has a very wide application. In the biblical culture, a “ruler” had great power to help or hurt, and so people would take great care to discern what kind of person he was so they could get the most advantage out of eating with him. But in today’s world, lots of people have the power or influence to be a blessing or make things difficult for someone. It could be a boss at work, a teacher, the chair of a committee, etc. In fact, in today’s world of social media when almost anyone can influence hundreds and perhaps thousands of people, it is a wise thing to do to “carefully discern” who you are with and the kind of person they are.