Keith joined the Religious Society of Friends (Quakers) in the 1660s, accompanying George Fox, William Penn, and Robert Barclay on a mission to the Netherlands and Germany in 1677.

In 1693, he and his fellow Keithians published An Exhortation & Caution to Friends Concerning Buying or Keeping of Negroes,[1] one of the earliest printed antislavery tracts in British North America.

Sponsored by the Society for the Propagation of the Gospel in Foreign Parts, Keith returned to the American colonies as a missionary from 1702 to 1704, trying to win over Quakers and others.

Keith joined the Religious Society of Friends (Quakers) in the 1660s, accompanying George Fox, William Penn, and Robert Barclay on a mission to the Netherlands and Germany in 1677.

For his survey work, the Proprietors gave him large grants of land including seven hundred acres in Monmouth County where he founded the town of Freehold (which broke off and became Marlboro).

[5] In 1693, he and his fellow Keithians published An Exhortation & Caution to Friends Concerning Buying or Keeping of Negroes,[6] one of the earliest printed antislavery tracts in British North America.

David Brion Davis, a leading scholar of abolition and slavery, argues that Keith's Exhortation foreshadowed "the major religious themes of nineteenth-century abolitionism.

[8] Sponsored by the Society for the Propagation of the Gospel in Foreign Parts, Keith returned to the American colonies as a missionary from 1702 to 1704, trying to win over Quakers and others.

[9] He preached in Williamsburg, Virginia in 1703, and left behind his daughter, Anne, who had likewise returned to the Anglican fold, unlike her husband, Quaker George Walker of Old Point Comfort.