Perkins  notes that the charge that the scribes “devour the houses of widows” (v. 40) also seems more characteristic of prophetic charges against the rich than of a particular role played by scribes. Some interpreters have hypothesized that scribes might have acted as guardians for widows who lacked male relatives. Others suggest that they may have accepted hospitality from widows under the pretense of piety in order to support their tastes for wealth and power. When he sent them out to preach, Jesus prohibited his own disciples from accumulating wealth or moving from the first household to take them in (6:8–10). Jesus also constantly warned his own disciples against seeking honor rather than serving others (9:33–35; 10:42–45). Mark’s Roman/Gentile readers were not likely to have had dealings with scribes, but they could recognize the same characteristics among others. The wandering Cynic philosophers who frequented Greco-Roman cities often castigated other philosophers whose wealthy patrons provided luxurious clothes, sumptuous food, and social honor.
“It describes the rich and powerful at their worst, much as the sharp social commentary that one finds in newspaper columnists. Every debater knows that if one can use a strong image to make opponents look ridiculous, the audience will have a hard time believing anything the opponents say. Of course, such comments must point to a real evil or social problem in order to be effective. Jesus insisted that his disciples not adopt social standards of power and influence. This depiction of the scribes applies to any religious authorities who treat their position as access to the influence and power of the wealthy, making those who should be defenders of the widow, the orphaned, and the poor the agents of their destruction. The condemnation for those who engage in such practices will be even worse than that for others, since they use the name of God to mask what they are doing.” [Perkins, 682]
It is unclear exactly what is meant by “devouring the houses of widows.” Chad Myers (Binding the Strong Man: A Political Reading of Mark’s Story of Jesus, 320-21) offers a couple of interpretations.
These are hard words, but they get harder. Scribal affluence is a product of their “devouring the estates of widows under the pretext of saying long prayers” (12:40). There are two possibilities for interpreting this bitter euphemism. Derrett [“’Eating up the Houses of Widows’: Jesus’ Comment on Lawyers?” NovTest, (1972) 14, pp. 1ff.] argues that Mark must be alluding to the practice of scribal trusteeship of the estates of widows (who as women could not be entrusted to manage their deceased husbands’ affairs!). Through their public reputation for piety and trustworthiness (hence the “pretext of long prayers”), scribes would earn the legal right to administrate estates. As compensation they would usually get a percentage of the assets; the practice was notorious for embezzlement and abuse. In this case the issue here would be similar to the korban practice to which Jesus objected in Mark 7:9-13. The vocation of Torah Judaism is to “protect orphans and widows,” yet in the name of piety these socially vulnerable classes are being exploited while the scribal class is further endowed.
Fledderman [“A Warning About the Scribes (Mark 12:37b-40).” CBQ, (1982) 44, pp. 52ff.] on the other hand believes that the explanation lies in Mark’s narrative opposition between “prayer” and “robbery.” The sites of scribal prayer is the temple, and the costs of this temple devour the resources of the poor. Jesus, who fiercely opposed such exploitation in the temple action and demanded a new site for prayer, points to the tragic story of the “widow’s mite” by way of illustration. Because of its narrative analysis this interpretation is probably the stronger one. In either case, however, the essential point is the same: scribal piety has been debunked as a thin veil for economic opportunism and exploitation. Mark charges them with full responsibility for these abuses, and in perhaps the harshest words in the gospel, announces that they will receive far heavier judgment (cf. 9:42).