"He shall from time to time give to the Congress Information of the State of the Union, and recommend to their Consideration such Measures as he shall judge necessary and expedient..."came to be interpreted as "Our Dear Leader shall, once per year, commandeer all our airwaves so that He might make the Divine Will known to us all. And then all the networks shall read the entrails of a goat. And there will be much rejoicing."
Thomas Jefferson, lor' bless him, thought that having the prez stand up and declaim in front of Congress was a bit too Ave, Caesar! for our young republic, and so he established the tradition of sending the annual report over to Congress in written form, the same way that I.N.C., Inc. lets shareholders know how things are going every year.
Then Woodrow Wilson, never one to miss a chance for a bit of public demagoguery, preferably draped in bunting, revived the practice of entering the House chamber in pomp and circumstance and laying down the law in person. With few exceptions, such as Silent Cal, the addresses have been public spectacles* ever since.
*Chastened by his recent drubbing at the polls, Jimmy Carter, a humble man with a great deal to be humble about, sent in a written outgoing address in '81, but it's been Speeches From The Throne from then on.