'Faithful' in the Bible

And I will raise me up a faithful priest, that shall do according to that which is in my heart and in my mind: and I will build him a sure house; and he shall walk before mine anointed for ever.

Then Ahimelech answered the king, and said, And who among all thy servants is so faithful as David, who is the king's son-in-law, and is taken into thy council, and is honorable in thy house?