What is the presidents purpose in the state of the union speech

Why does the President give a State of the Union speech?
The Constitution (Article 2, Section 3) requires him to "from time to time give to the Congress information on the state of the Union". This does not have to be an annual event but has become so by custom and it does not have to be a speech,
but that is what people expect now and it gets great press coverage so it has become a political necessity.