The adoption of a new rule of faith in the seventeenth century significantly changed the way English-speaking Protestants perceive the doctrine of the Trinity. Having been the proper personal name by which Christians came to know and love their God, the Trinity became primarily a rational construct and as such no longer clearly mattered for salvation. In Invocation and Assent Jason Vickers charts this crucial theological shift, illuminating the origins of indifference to the Trinity found in many quarters of Christianity today.