Mat 23:1 Then spake Jesus to the multitude, and to his disciples,
Moses was the lawgiver, a true servant of God who spoke the words THE LORD gave unto him in the ears of all the people.
Mat 23:2 Saying, The scribes and the Pharisees sit in Moses' seat:
But the point Jesus is now making is that Moses seat, his authority as the lawgiver, has been taken over by those who claim to be true servants of God, even claiming to be children of Abraham throught the house of Judah, but who are liars and are of the synagogure of Satan (Rev 2:9 & Rev 3:9).
In the books Era and Nehemiah know that at one point when the remnant of Judah and Benjamin were on their way back to rebuild the temple in Jeruslem, Ezra stopped and took a census of the people and there was not one Levitical Priest among the entire lot to perform the priestly duties in the temple. So Ezra sent a "nethinim"( temple servant) back to Babylon to get some true priests.
When Christ arrived on the scene the temple had been taken over by the temple workers, even the kenites, the sons of Cain, who now sat in authority as those whose were to keep the law and speak His words to the people.
Mat 23:3 All therefore whatsoever they bid you observe, that observe and do; but do not ye after their works: for they say, and do not.
Jesus Christ is NOT saying do whatsoever these scribes and Pharisees bid you to do. Meaning if it is true and alighs with Gods Word and not after the traditions of men, that do!
The scribes and Pharisees say, and do not, meaning they say they are doing the will of God as His representatives, but they do not do the will of God.
So we as to Observe and discern between that which is clean and that which is unclean knowing the these fakes who sit in the authority (seat) of Moses, say they teach the law, the truth God's Word, but the words the teach are not His!
Observe, tereo, Gk 5083 from teros(a watch, perhaps akin to gk 2334 (theoreo); to guard (from loss or injury, properly by keeping the eye upon.
God's word sets us free John 8:32. However, the traditions of men set burdens upon the people.
Mat 23:4 For they bind heavy burdens and grievous to be borne, and lay them on men's shoulders; but they themselves will not move them with one of their fingers.
Mat 23:5 But all their works they do for to be seen of men: they make broad their phylacteries, and enlarge the borders of their garments,