People often lived (and still do) by the false concept that somehow being from a certain bloodline means that you are good - and that you don't need a Messiah to forgive your sins.  Jesus's teaching, in the Temple, is 100% contrary to this lie and He is attempting to correct their bad theology by declaring they need to believe, and from that believe we are called to abide (dwell, to live in) His teachings.  If we are truly going to get serious about Discipleship, it must start here with this important teaching to the people of Israel - as well as to us right now wherever we might hear these words.  God bless you.