A lineage is like a spiritual battery connecting the true enlightened mind of another master of the same clan with the next successor. They carry this tradition much like a sacred pearl of true awareness. They are connected to all the minds of the awakened ones in the lineage going back to the very first master who created the lineage.
In an oral tradition, secret instructions are passed from one master to another master keeping the integrity of the art whole and undiluted. There are outer, inner and secret teachings.
Without a true lineage, enlightenment in these modern days are next to impossible.