If the BIble is not error-free, then what is Christianity all about?

Quoting the Catholic Encyclopedia farley ed vol iii p712,
"Our documentary sources of knowledge about the origins of christianity and its earliest develeopment are chiefly the New3 Testament scriptures, the AUTHENTICITY of which we must, to a great exgent, take for granted."

Taken for granted. without any supporting backup from prestigious history books. why?

... continues the Cath Encyclo pp 655-6, the Church admits "... that the Gospels do not go back to the first century of Christian era"

if so, where did it come from? legendary tales from pagan cults?