People often ask me what I mean by "sincerity." Applying the usual definitions doesn't help a great deal when we're using the word in a Buddhist context.
Merriam-Webster's Online Unabridged Dictionary defines sincerity as "the quality or state of being sincere." They define sincere as:
"marked by genuineness: as a: free of dissimulation : not hypocritical; b: (1) free from adulteration : not mixed (2) : not containing any foreign element; c : marked by truth; d : motivated by a desire for meaningful expression."
Ven. Master Chin Kung gives a much simpler—and for us a much more helpful—definition:
Sincerity is no wandering thoughts.
Sincerity in helping others means no wandering thoughts, no selfish thoughts.
Sincerity in listening means no wandering thoughts, no thoughts of "I" or "me" or "mine."
Sincerity in teach others means no wandering thoughts, no thoughts of self-benefit.
Sincerity in chanting means no thoughts other than "Amituofo."