Matthew 23:15 The Pharisees' converts were attracted to Phariscism, not to God. By getting caught up in the details of their additional laws and regulations, they completely missed God, to whom the laws pointed. A religion of works puts pressure on people to surpass others in what they know and do. Thus, a hypocritical teacher was likely to have students who were even more hypocritical. We must make sure we are not creating Pharisees by emphasizing outward obedience at the expense of inner renewal.
Matthew 23:23, 24 It's possible to obey the details of the laws but still be disobedient in our general behavior. For example, we could be very special and faithful about giving 10% of our money to God, but refuse to give one minute of our time in helping others. Tithing is important, but giving a tithe does not exempt us from fulfilling God's other directives.
Matthew 23:24 The Pharisees strained their water so they wouldn't accidentally swallow a gnat - an unclean insect according to the law. Meticulous about the details of ceremonial cleanliness, they nevertheless had lost their perspective on inner purity. Ceremonially clean on the outside, they had corrupt hearts.
Matthew 23:25-28 Jesus condemned the Pharisees and religious leaders for outwardly appearing saintly and holy but inwardly remaining full of corruption and greed. Living our Christianity merely as a show for others is like washing a cup on the outside only. When we are clean on the inside, our cleanliness on the outside won't be a sham.