What does this mean It must be by his death and for your part you know no personal cause to spurn?

This phrase suggests that the speaker believes a significant action or change must occur as a result of someone's death. The mention of "no personal cause to spurn" implies that the listener has no personal grievances or reasons to reject or resist this outcome. Essentially, it highlights the inevitability of the situation and the listener's position of acceptance or obligation regarding it.