This passage is found in the Revised Common Lectionary Year B (Most recently Nov 8, 2015)
Summary: This is a case where the Greek does not alter the meaning, but simply forces us to slow down and examine Jesus' familiar words. As I read the passage this time, I became struck by Jesus' condemnation of an overly consuming, self-aggrandizing and elitist clergy. While I believe the office of ministry is a divine institution, I know that I personally can err very much in my execution of this office. More generally, I think Jesus makes a comment on our consumption and our giving this day, a message that all of us need to hear.
βλεπω (12:38; "see") The word here for "watch out" is simply the Greek 101 for see; Jesus will tell his followers to "watch out" five times in this section (12:38, 13:5;9;23;33).
γραμματευς (12:38; "scribes") This word has an obvious English cognate: "Grammar." The question for us today is, whom do we need to watch out for -- who are the grammarians today? I struggle with this question a bit more personally -- how do I become a grammarian, who says "no" to the working of the Lord, either in my congregation or in my denomination? How do I NOT become someone whom Jesus warns against. The further description of Jesus' critique includes:
they wear στολη (12:38, "stole" or "robe)
and sit in the
προτοκαθεδρια (12:39, "first seat"). Ouch.
κατεσθιω (12:40, "devour") As you guessed, the Bible uses this word in an entirely negative fashion. It also comes up in the prodigal son, where the son has consumed the father's property (literally, βιος, used also in this passage in vs. 44). One can read this passage as a narrow critique of 1st century Jewish leadership, more broadly of religious leaders over time, or most broadly, against all over-consumption. In what ways does our whole culture "devour widows houses while praying long prayers." A prophetic voice is helpful here, but I think Jesus also calls each us to examine our own actions.
βιος (12:44, "life" The woman gives "the whole of her life" The word life here is "bios." So the sermon is not about stewardship, but about biology. Or maybe better put, Stewardship includes biology. Do we live to consume (food and status) or give of our whole life?
Grammar note: Here we have a substantive participle "the ones who devour" and a participle that might also be adjectival (in this case, the ones who devour = the ones who pray) or circumstantial. See, it can go both ways because the participle "pray" does not have an article in front of it. Normally you translate this type of participle as a circumstantial participle, one that describes the circumstances under which the main action takes place. If translated in this fashion, it would read, "the ones who devour widows houses while praying long prayers." Ouch! I think in this case, the circumstantial participle gives a better feel for their hypocrisy: They pray while they sin.