The commentary on Milton's eighteenth sonnet ("On the Late Massacre' in Piedmont") is rich and extensive. Kester Svendsen's often cited 1945 essay, the first close reading of the poem; ushered in many other interpretations of its biblical imagery, as well as speech-act analyses, reader- response discussions, and at least one Foucaldian study. Yet even though a religious conflict inspired the sonnet, and although numerous interpreters have paid close attention to the work's biblical texture, no sustained theological account of the poem has been offered. The present essay seeks to fill that gap by examining the work in light of two heresies that Milton was probably thinking through when he wrote the poem, namely, Mortalism and Traducianism.
Mortalism holds that, at death, the soul dies (or, in some versions, sleeps) with the body, and that both are resurrected at the end of the age. Traducianism (from Latin tradux, a shoot or sprout) is Mortalism's correlative. Like Mortalism, it assumes that the soul is corporeal, but while Mortalism draws out the logical consequences of that assumption for the end of life, Traducianism does so for its beginning, claiming that the soul is passed from one generation to the next in the act of intercourse. Milton considers each idea at length in De Doctrina Christiana, and John Shawcross surmises that the poet's thinking about the two concepts solidified between 1647 and 1655. The sonnet was probably composed in May or June 1655.
Burbery, Timothy J. “From Orthodoxy to Heresy: A Theological Analysis of Sonnets XIV and XVIII.” Milton Studies 45 (2006): 1-20.