Matthew 16:1 says, The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven.  The Pharisees were back, and this time the Sadducees were with them.  Once more they were demanding as sign from heaven to prove that Jesus was Who He said He was.  Jesus had already told them that the only sign there would be was His death, burial, and resurrection.  Faith in that fact is the only sign we will have today also.  In verse two Jesus says, He answered and said unto them, When it is evening, ye say, It will be fair weather: for the sky is red.  Jesus asked the Pharisees and Sadducees if they could read the signs of the weather.  A red sky in the evening would be interpreted as meaning fair weather was ahead.  Verse three continues, And in the morning, It will be foul weather to day: for the sky is red and lowring. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?  Jesus said that a red sky in the morning would mean fair weather was coming.  These were signs to the people about weather, but they may not have always held true.  The sign that Jesus had said would be the only sign given, His death, burial, and resurrection would and always will be true.  We simply have to accept that fact.  Jesus called the Pharisees and Sadducees hypocrites.  If we come to Jesus today demanding physical signs instead of simply coming to Him by faith, we are being hypocritical.  In verse four Jesus declares, A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.  Jesus declared the Pharisees and Sadducees to be a wicked and adulterous generation, though they considered themselves to be some of the most righteous of those who called themselves God's people.  As already stated, Jesus said the only sign would be His death, burial, and resurrection.  Verse five says, And when his disciples were come to the other side, they had forgotten to take bread.  The disciples once more found themselves unprepared.  They had forgotten bread.  As we are serving Christ, we may at times realize that we don't have something that we need, but if so, we need to simply look to God to supply our need.  Verse six says, Then Jesus said unto them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.  I believe that Jesus was actually warning the disciples to not pay heed to what the Pharisees and Sadducees said was the way to a spiritual life with God.  The warning was really against allowing false teachings to enter into the gospel message.  Verse seven states,  And they reasoned among themselves, saying, It is because we have taken no bread.  The disciples were still thinking in physical, or worldly, terms.  They thought Jesus was speaking about their not bringing bread, but instead of asking Jesus to clarify what He was saying, they reasoned among themselves.  If we have a question about what Jesus is instructing us to do, then our best course of action is to ask Him.  Others may lead us astray if we reason together with them, but Jesus never will.  Verse eight declares, Which when Jesus perceived, he said unto them, O ye of little faith, why reason ye among yourselves, because ye have brought no bread?  Just as Jesus knew the concern of the disciples, so He knows ours today.  We, like the disciples, display a lack of faith when we fail to go to God with our concerns.  In verse nine Jesus asks, Do ye not yet understand, neither remember the five loaves of the five thousand, and how many baskets ye took up? Then He continues in verse ten, Neither the seven loaves of the four thousand, and how many baskets ye took up?  Jesus had just fed a multitude on two occasions, which is a clear statement that it was not the same miracle told twice.  Jesus asked if the disciples had forgotten this already, and therefore thought that Jesus was worried about bread.  When we find ourselves needing something to continue in our work for God, we need to remember that He never has and never will fail to provide for our needs.  Verse eleven asks, 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?  Jesus asked the disciples why they didn't understand that He was not speaking of bread when He issued His warning about the Pharisees and Sadducees.  We need to always look for the spiritual reason behind what God is telling us.  Verse twelve states, 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.  The disciples finally understood what Jesus was telling them when they listened to Him instead of reasoning among themselves.  Jesus was warning them about the doctrine of the Pharisees and Sadducees.  We today need to listen to what God has to say to us, and not to what the world has to say about God.