The word faithfulness in Hebrew is EMUNAH and the action of the verb root is "to lean on." There are 3 things that are testimonies or proof that God is faithful: 1) the heaven and the earth, 2) his Word, and 3) his covenants and promises. "There is no shadow of turning with thee; Thou changest not, thy compassions they fail not (Lamentations 3:21-23).