Think about being faithful. What does it mean to be full of faith?
Some synonyms to faithful are to be steadfast, constant, loyal, and remain true to. The root word faith means “a strong belief; complete trust or confidence in someone or something”. We might then say that being faithful means to be so convinced and trusting that we put full confidence in someone or something to the point where we remain true, constant, steadfast, and loyal to it or him/her. We can see from these definitions that faithfulness involves all our mind, emotions, and actions and with strong conviction and motivation.
I would say that faith and faithfulness is motivated by love and what is believed as truth. It is a strong relationship!