That says nothing about the country being founded on religion.
If only he had actually read the entire Declaration of Independence, he would have found that the Declaration of Independence didn't actually found the nation. It even says so in the document.
We, therefore, the Representatives of the UNITED STATES OF AMERICA, in General Congress, Assembled, appealing to the Supreme Judge of the World for the Rectitude of our Intentions, do, in the Name, and by the Authority of the good People of these Colonies, solemnly Publish and Declare, That these United Colonies are, and of Right ought to be, Free and Independent States; that they are absolved from all Allegiance to the British Crown, and that all political Connection between them and the State of Great-Britain, is and ought to be totally dissolved; and that as Free and Independent States, they have full Power to levy War, conclude Peace, contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do. And for the support of this Declaration, with a firm Reliance on the Protection of the divine Providence, we mutually pledge to each other our Lives, our Fortunes, and our sacred Honor.
This renounces their ties to the Crown and expresses their solidarity in their fight for independence. At this point the states are
not unified, other than in name and in their common struggle. Note that each state still has the right to independently raise taxes and levy war. If it was left at that then we would have ended up with 13 different countries.
The nation would not be formed until the Constitution was written. The first line of the Constitution clearly states in the words of our Founders the fundamental principle of our nation.
We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.
???
The Declaration of Independence does not create a nation. It even says so in the title "Declaration of
Independence," not "Declaration of
Nation." The Declaration of Independence is literally a list of all the complaints against England and a statement of the
intent to break away from the country and form and
independent nation. It's important to note that at no point does the Declaration of Independence
form a nation.