From: Matthew 23:13-22
Jesus Indicts the Scribes and Pharisees
(Jesus said to the scribes and Pharisees,)  "But woe to you, scribes and Pharisees, hypocrites! because you shut the Kingdom of Heaven against men; for you neither enter yourselves, nor allow those who would enter to go in.  Woe to you, scribes and Pharisees, hypocrites! for you traverse sea and land to make a single proselyte, and when he becomes proselyte, you make him twice as much a child of Hell as yourselves.
 "Woe to you, blind guides, who say, `If any one swears by the temple, it is nothing; but if any one swears by the gold of the temple, he is bound by his oath.'  You blind fools! For which is greater, the gold or the temple that has made the gold sacred?  And you say, `If any one swears by the altar, it is nothing; but if one swears by the gift that is on the altar, he is bound by his oath.'  You blind men! For which is greater, the gift or the altar that makes the gift sacred?  So he who swears by the altar, swears by it and everything on it;  and he who swears by the temple, swears by it and by him who dwells in it;  and he who swears by Heaven, swears by the throne of God and by Him who sits upon it."
13. Here comes our Lord's invective against the behavior of the scribes and Pharisees: His "woes" condemn their past conduct and threaten them with punishment if they do not repent and mend their ways.
14. As RSV points out, "other authorities add here (or after verse 12) verse 14, "Woe to you, scribes and Pharisees, hypocrites! For you devour widows' houses and for a pretense you make long prayers; therefore you will receive greater condemnation." Our Lord is not reproaching them for praying long prayers but for their hypocrisy and cupidity. By going in for a lot of external religious practices, the Pharisees wanted to be recognized as devout men and then trade on that reputation particularly with vulnerable people. Widows, for example, would ask them to say prayers; the Pharisees in turn would ask for alms. What Jesus means here is that prayer should always come from an upright heart and a generous spirit.
15. "Proselyte": a pagan convert to Judaism. The root of the word means "he who comes", he who--coming from idolatry--joins the chosen people in response to a calling from God. The Pharisees spared no effort to gain converts. Our Lord reproaches them not for this, but because they were concerned only about human success, their motivation being vainglory.
The sad thing about these proselytes was that, after receiving the light of Old Testament revelation, they remained under the influence of scribes and Pharisees, who passed on to them their own narrow outlook.
22. Our Lord's teaching about taking oaths is given in the Sermon on the Mount (Matthew 5:33-37). Jesus does away with the nitpicking casuistry of the Pharisees by focusing directly on the uprightness of the intention of the oath-taker and by stressing the respect due to God's majesty and dignity. What Jesus wants is a pure heart, with no element of deceit.
Our Lord particularly reproves any tendency to undermine the content of an oath, as the Doctors of the Law tended to do, thereby failing to respect holy things and especially the holy name of God. He therefore draws attention to the commandment of the Law which says, `You shall not take the name of the Lord your God in vain" (Exodus 20:7; Leviticus 19:12; Deuteronomy 5:11).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.