Mark twain quoted daniel webster as saying, "i still live" in order to:

give an example of a great man's dying words.

Explanation:

According to twain, the dying words of a great man will will be learned by other individuals and they will make it applicable in their life.

After that person die, the principles that that great man teach will be embodied by other person. Because of this, we can infer that the great man is still live even though he is no lounger physically present in this world.