'Sincerity' in the Bible

“Now, therefore, fear the Lord and serve Him in sincerity and truth; and put away the gods which your fathers served beyond the River and in Egypt, and serve the Lord.

He who walks righteously and speaks with sincerity,He who rejects unjust gainAnd shakes his hands so that they hold no bribe;He who stops his ears from hearing about bloodshedAnd shuts his eyes from looking upon evil;