Jesus continues his attacks on the Pharisees and Scribes. We should see this as a criticism of the legalistic mind. Not all the Pharisees and Scribes were hypocrites, and we can find their like in our own Christian communities, and Matthew is likely thinking of Christian Pharisees rather than those who criticized Jesus.
In today's reading, Jesus makes two points. First, he accuses Pharisees of being scrupulous about the tiniest regulations while being neglectful of much more important issues such as judgement, compassion and faithfulness to God's will. They strain out tiny insects (which were regarded as 'unclean') from their drinking water but then "swallow the camel", that is, ignore the essential things like loving all our brothers and sisters, practising forgiveness and taking care of the poor and needy.
In the second part, he criticizes them for focusing only on the externals - their image and what people could see - so that they could be admired for their observance of the Law. But they are like whitewashed tombs, lovely on the outside but inside are full of stench and corruption.
There is no real similarity between what appears on the outside and what they are inside. How many of us have perfect integrity? Do people see what is going on inside of us?
Blessed are the pure in heart, for they will be called the children of God!