Washington recognized America was a country of Christian Europeans with common cause and goals and it was important to keep it that way.
"With slight shades of difference, you have the same religion, manners, habits, and political principles. You have in a common cause fought and triumphed together. The independence and liberty you possess are the work of joint councils and joint efforts, of common dangers, sufferings, and successes."
From his farewell address.
https://www.presidency.ucsb.edu/documents/farewell-addressAlso
"The unity of government which constitutes you one people is also now dear to you. It is justly so, for it is a main pillar in the edifice of your real independence, the support of your tranquillity at home, your peace abroad, of your safety, of your prosperity, of that very liberty which you so highly prize. But as it is easy to foresee that from different causes and from different quarters much pains will be taken, many artifices employed, to weaken in your minds the conviction of this truth, as this is the point in your political fortress against which the batteries of internal and external enemies will be most constantly and actively (though often covertly and insidiously) directed, it is of infinite moment that you should properly estimate the immense value of your national union to your collective and individual happiness; that you should cherish a cordial, habitual, and immovable attachment to it; accustoming yourselves to think and speak of it as of the palladium of your political safety and prosperity; watching for its preservation with jealous anxiety; discountenancing whatever may suggest even a suspicion that it can in any event be abandoned, and indignantly frowning upon the first dawning of every attempt to alienate any portion of our country from the rest or to enfeeble the sacred ties which now link together the various parts."
And also Washington and of course he was speaking of the opinion of the time by all the founders recognize that religion ( which I'll remind you he expressed in the same speech above was the common religion of Christianity which differed very little among the people of the country when it was formed) must be part of the government. The absolute opposite of the argument made today that should be excluded from government.
"Of all the dispositions and habits which lead to political prosperity, religion and morality are indispensable supports. In vain would that man claim the tribute of patriotism who should labor to subvert these great pillars of human happiness--these firmest props of the duties of men and citizens. The mere politician, equally with the pious man, ought to respect and to cherish them. A volume could not trace all their connections with private and public felicity. Let it simply be asked, Where is the security for property, for reputation, for life, if the sense of religious obligation desert the oaths which are the instruments of investigation in courts of justice? And let us with caution indulge the supposition that morality can be maintained without religion. Whatever may be conceded to the influence of refined education on minds of peculiar structure, reason and experience both forbid us to expect that national morality can prevail in exclusion of religious principle."
Thus we have the man who was perhaps one of the most instrumental in the founding and discussions and writing of the Constitution and implementing it and its first president stating unequivocally that America was a Christian Nation composed of people of common origin meaning Europeans and that preservation of religion meaning that Christian religion of course in the government was essential and was the intention is f the founders.
(It's important to recognize at this time that jews were commonly excluded from request for citizenship in the new nation. Even very wealthy ones constantly petitioned the states and the federal government to be allowed to be a citizen of the nation were excluded because the founders knew their jewish beliefs and actions conflicted with the Christian morality of the nation.)
This was not just any speech from washington. This was Washington's farewell address where he used the sum of all his accumulated knowledge and his first terms as the first president of the United States to State these facts and summarize what he thought was the most important messages to those who would carry on.
https://www.presidency.ucsb.edu/documents/farewell-address
