How does the Tennis Court Oath relate to the French Revolution?

The Tennis Court Oath essentially marked the real beginning of the French Revolution. When the Third Estate was knocked out of the meeting of the First and Second Estates, they moved to a nearby tennis court where they declared themselves the National Assembly and swore never to separate until they had drafted a constitution for France.

By declaring that they had the power to remake the government, the National Assembly became a group not only joined in protest against Louis XVI's despotic rule, but joined under the assertion of having sovereign power in the nation.

The Tennis Court Oath was what began the real revolutionary action that was soon to come.