Why is resolved used to begin the second paragraph of the preamble

Beginning a sentence with the word "Resolved" is a short form to say "It is resolved" or "we have resolved that...". It means that the Senate and the House of Representatives reached to an agreement about the topics discussed in that paragraph.

Prince Estabrook played an important role in Revolutionary War history as the first African-American soldier to fight for the Continental Army. Estabrook was born in the 1740's into slavery. His owner, Benjamin Estabrook, operated a grist mill near Lexington. Prince Estabrook took part in the Lexington Militia, called the Lexington Minute Men, which fought against the British on April 18, 1773. His owner had given him permission to be a part of the militia. During the battle, he was struck on the left shoulder. He recovered, and fought in several other Revolutionary War battles. He was emancipated after his service in the Army, and died around age 90. He has a memorial to his service on Lexington Green.