What is the meaning of the the Prophet's saying (Hadith): "Do not belittle any good deed, even meeting your brother with a cheerful face"?

Do not belittle any good deed, even if it is small, for everything deemed good by Islamic law and reason is indeed good. Examples of this include: giving water to someone who needs it, even from your own bucket, and meeting your Muslim brother with a cheerful and pleased face, not a scowling or angry one. For humility and gentleness are signs of good character and perfect piety.