The opposite of sincere is…being hypocritical, insincere, false-faced, masked to hide – all of these are the wisdom of men, unspiritual, demonic.

  What does the LORD hate?
(NIV) Proverbs 6:16-19 “There are six things the LORD hates, seven that are detestable to him:
17    haughty eyes, a lying tongue, hands that shed innocent blood,
18    a heart that devises wicked schemes, feet that are quick to rush into evil,
19    a false witness who pours out lies and a man who stirs up dissension among brothers.” 

  What a list!  The above is what is produced from being a hypocrite, a person who is insincere.
  Hypocrisy was condemned by Jesus in the strongest of terms and was directed at religious leaders.  (See Matthew 6:5, 16; 23:13, 15, etc)

  Sincerity is being honest, forth-right, truthful with nothing to hide, discrete (discretion is using wisdom wisely).
  Where in our communications, our phone calls, e-mails, texting and twittering are we insincere? 
  What freedom there is when we do not need to be concerned about what we have said in the past and the need to “cover-up”.  Insincerity and hypocrisy are associated with pride, lies, etc…look at the list from Proverbs 6:16-19.

 Pure and wholesome thinking is in direct contrast to how those without Godly wisdom think and act.
  God is trustworthy for He is sincere and without hypocrisy.  God’s word is the same in the Old Testament as in the New Testament.  No one has to guess if God has changed His mind or His words.

~Godly wisdom is sincere~