'Faithful' in the Bible

And I will raise me up a faithful priest, that shall do according to that which is in mine 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 is so faithful among all thy servants as David, which is the king's son in law, and goeth at thy bidding, and is honourable in thine house?