Gaius had to believe in Merlin's power and wit. He had run out of ideas and his medicinal knowledge was useless, but there was still something he could be good for. The hard work he did for Camelot on a daily basis and the lack of recognition for it were taking their toll on the young sorcerer and the physician had to make sure he didn't lose heart.
Destiny, the future of Albion and Arthur were his faith. Gaius had to be his guide, the rock he could lean on when he felt weary. He had to be his strength.