Today's passage is a good reminder to us of what Jesus thought was important.
He tells his listeners to beware of the scribes. In their time, they were more educated than most people, they devoted time to reading the Scriptures, and, consequently were capable of interpreting God's message to people who couldn't read as well or didn't have the time to devote to thinking about how to act Scripture's intention to their lives.
God' people have always and continue to benefit from articulate scholars. Yet, Jesus is warning his audience to beware of them.
He begins by pointing out that they wear obviously high class clothes and are greeted with respect.
That is, who society thinks are of higher value than the rest of us, who act and look like society should feel that way, are not necessarily the ones that are doing what God intends for us to do.
The specific examples of inappropriate behavior are (1) they misappropriate the assets of the powerless and (2) for appearance sake, they say long prayers.
And they knew better. They read the scriptures a lot. They must have seen the many references the prophets had made about the poor, about orphans and widows; e.g., Isaiah 1:17, 23; Jeremiah 7:6; 22:3; Zechariah 7:10: Malachi 3:5.
Morna Hooker sums up Jesus' warning in her commentary that I recommend to you, The Gospel According to Saint Mark:
The answer can be suitably summed up by reference back to vv.28-34; those who parade their piety are merely guilty of silly ostentation, but those who oppress the defenceless are certainly failing not only to love God, but also to love their neighbor.