In this passage there is a simple message and the Messiah was very clear in His monolog. There are few places in the scriptures where He was stronger with His words. Christ is speaking to the scribes, Pharisees and teachers, religious leaders who were all the targets of this discourse.
The warning to this group was to those who sat in the Moses seat(leaders of the church), where the holy scriptures were both read and taught (seat of authority). Their teachings were focused around the outward practices, it must make us look good to be good. These teachings put the hearers under bondage and weighted down the people with rituals. For instance, washing the outside of the cup that everyone sees, the outward was what mattered to them but the problem is that Jesus wasn't hearing any talk or interest about cleaning the inside of the cup. It was all about looking good for ego sake. Jesus is saying here, yes clean the cup on the outside, as well as the inside. It needs the same focus as the outside. Then there were the issues of saying one thing and doing the another, along with showing superiority by their position and power, which is pride.
Today that same warning applies to us all to ensure that the whole truth is presented, the outer... and the inner part.
Woe to those that mislead, or exploit the word of God.