Beware of Pharisees & Sadducees.

After the church leaders had asked Jesus for a sign from heaven to prove he was the Son of God, Jesus said to his disciples, " “Watch and beware of the leaven (doctrines) of the Pharisees and Sadducees.”

Jesus said of the Pharisees, "You leave the commandment of God and hold to the tradition of men.” Mark 7:8 He also called them "hypocrites," which meant they looked religious but were not godly. They had a form of religion that meant nothing.

The name Pharisee in its Hebrew form means separatists, or the separated ones. They were also known as chasidim, which means loyal to God, or loved of God - extremely ironic in view of the fact that by His time, they made themselves the most bitter, and deadly, opponents of Jesus Christ and His message.

The Pharisees perhaps meant to obey God, but eventually they became so devoted and extremist in very limited parts of The Law (plus all that they themselves added to it), that they became blind to The Messiah when He was in their very midst. They saw His miracles, they heard His Words, but instead of receiving it with joy, they did all that they could to stop Him - eventually to the point of getting Him killed because He truthfully claimed to be the Son of God.

http://www.keyway.ca/htm2002/pharisee.htm

Jesus said of the Sadducees, "Jesus said to them, “Is this not the reason you are wrong, because you know neither the Scriptures nor the power of God?

For the Sadducees say that there is no resurrection, neither angel, nor spirit: but the Pharisees confess both" Acts 23:8

The Sadducees were one of the major sects of Judaism at the time of the first coming of the Messiah. Along with the Pharisees and the Herodians, the Sadducees formed the religious council of authority in Jerusalem - whose disparate beliefs and teachings had drifted far from what the LORD had commanded to their fathers 

http://www.keyway.ca/htm2012/20121219.htm

So, if the disciples were to beware of the teachings of Pharisees and Sadducees then we also should beware.

We should beware of legalism, self-righteousness and exclusiveness. We should beware of not knowing and believing the scriptures. We should beware of asking for a sign from heaven and ignoring all the signs God has already given to the world. We should beware of rejecting God's messengers and wanting to kill them; for this is what envy and unbelief led the Pharisees and Sadducees to do.