Interpretation of any work is based solely upon Reader-Response. Therefore, many different justifiable interpretations of a text can be made and still hold water based upon the fact that, many times, readers do not come to the same conclusions regarding interpretations of a text.
James Shirley's poem "Death the Leveller" is a poem which depicts the fact that Death does not care if one is a king or a peasant. Given this fact, Death comes for all in the same way. In the end, all will turn to dust whether king or not.
Important lines which show this fact are:
Death lay its icy hands on kings:
And in the dust be equal made.
These lines depict what was stated above--regardless of nobility, when Death comes, all are equal.
The line "some men with swords may reap the field" refers to war. Men will come together in war to "reap" (harvest) those who fight against them. In the end, regardless of who may be the strongest, all "must give up their murmuring breath" and "creep to death."
Again, the reference to the fact that Death will eventually take all who live is made here.
The last stanza refers to the fact that regardless of any "mighty deeds" one may have accomplished, all will lay their heads "upon Death's purple alter."