The Pharisees and Sadducees came, and to test Jesus they asked him to show them a sign from heaven.  He answered them, "When it is evening, you say, 'It will be fair weather, for the sky is red.'  And in the morning, 'It will be stormy today, for the sky is red and threatening.'  You know how to interpret the appearance of the sky, but you cannot interpret the signs of the times.  An evil and adulterous generation asks for a sign, but no sign will be given to it except the sign of Jonah."  Then he left them and went away.

(see identical passage: Matthew 12.38-39)

Man can be very crafty when it comes to interpreting earthly, natural signs.  Here Jesus rebukes us for not applying wisdom to interpret heavenly, supernatural signs.  It is fine to have a mind of reason as we approach the day but we must also have a heart of faith.

Even though he rebuked them he still promised the Pharisees and Sadducees the greatest sign of all: his own death and resurrection.  His resurrection after three days in the tomb is the final, definitive sign which Christ gave to us during his time on earth that God's kingdom has come upon man.  Do we believe and live that mystery or are we caught up in purely natural phenomenon?  Perhaps in our hearts we believe Christ's death and resurrection was a historical reality but has no bearing on our lives of today.  If we think that way it is only because we have not experienced the tomb in our own lives and united it to Christ's sepulcher in order to be united to his resurrection in our baptism.

Make Christ's death and resurrection your own and begin to live the spiritual realities of God's kingdom among man.