(When a wholly detached expression or sentence is parenthesized, the final stop comes before the last mark of parenthesis.)
Quotations. Formal quotations, cited as documentary evidence, are introduced by a colon and enclosed in quotation marks.
The provision of the Constitution is: “No tax or duty shall be laid on articles exported from any state.”
Quotations grammatically in apposition or the direct objects of verbs are preceded by a comma and enclosed in quotation marks.
I recall the maxim of La Rochefoucauld, “Gratitude is a lively sense of benefits to come.”
Aristotle says, “Art is an imitation of nature.”
Quotations of an entire line, or more, of verse, are begun on a fresh line and centered, but need not be enclosed in quotation marks.
Wordsworth's enthusiasm for the Revolution was at first unbounded:
Bliss was it in that dawn to be alive,
But to be young was very heaven!