"Give not that which is holy to the dogs, nor throw your pearls to the swine; otherwise the swine will trample them under their feet and the dogs turn and maul you."  Matthew 7:6  (Weymouth translation). No one would give real pearls to swine, so what pearls is Jesus talking about? He explains the meaning of pearls in Matthew 13:45 (NIV), "Again, the kingdom of heaven is like a merchant looking for fine pearls.  When he found one of great value, he went away and sold everything he had and bought it." 

Jesus, speaking in parables, compared his message of the kingdom of God to fine pearls.  He did not expect the selfish, sensual, earthly-minded people (dogs, swine) to be able to understand or appreciate the truths He was preaching. Jesus was thus instructing us to use the spirit of a sound mind to discriminate between those who might receive the truth into tender hearts and those who might mock us and become enraged by the truth.  

But does not our Heavenly Father desire all to be saved and come to a knowledge of the Truth? (1 Timothy 2:4)

Indeed God does. But there is a season for everything and from this direct instruction from Jesus we can see that some are better off left in ignorance for the present until the experiences of a life without God shall have touched their hearts and prepared them to receive the Gospel.