Richard Henry Lee wrote the actual declaration that was passed by the Congress on 2 July 1776. The proclamation of that Declaration was written by Jefferson (with lots of edits). The purpose of the proclamation was political, primarily designed to publicly state the reasons for Congress' action of 2 July 1776 and to appeal to foreign governments for assistance.
Interestingly, on July 4 the Congress also tasked Franklin and Jefferson to come up with a great seal for the United States. Franklin came up with the parting of the Red Sea by Moses, and Jefferson was focused on the Children of Israel led by Cloud by day and Pillar by night. Jefferson came around to Franklin's viewpoint.
Each day's proceedings was bounded by prayer, so the July 2 declaration of independence was in the context of that same Congress that in the spring of 1776 called for this: (note the reference to Jesus Christ and the call to Christians)
