Matthew 16

The Savior warned His disciples -

"Take heed and beware of the leaven of the Pharisees and of the Sadducees."  (New Testament | Matthew 16:6)

When they did not seem to understand, the Savior followed up  -

"How is it that ye do not understand that I spake it not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?
12 Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees."  (New Testament | Matthew 16:11 - 12)

In symbolism, the Savior taught that we must beware of false doctrine.  Much like leaven, as it is mixed through out the true doctrine, it grows and expands.  We see this in many cases of religion.  The Savior taught the true doctrine of -

"If any man will come after me, let him deny himself, and take up his cross, and follow me.
25 For whosoever will save his life shall lose it: and whosoever will lose his life for my sake shall find it.
26 For what is a man profited, if he shall gain the whole world, and lose his own soul? or what shall a man give in exchange for his soul?
27 For the Son of man shall come in the glory of his Father with his angels; and then he shall reward every man according to his works."  (New Testament | Matthew 16:24 - 27)

Works being receiving the ordinances and covenants and do God' will or keep His commandments.