What was significant about the battles of Lexington and Concord?
The main significance of these two battles is that they were the first two armed conflicts of what became the Revolutionary War. The battles were not particularly significant in military terms, but they were the first battles of the war.
In the time since the passage of the “Intolerable Acts” after the Boston Tea Party, the colonists in Massachusetts had been making at least some preparations for war. They had, for example, been stockpiling things like gunpowder and ammunition. By the spring of 1775, the colonial leaders had created such a stockpile in Concord. The British in Boston had gotten wind of the existence of the cache. They decided to march to Concord to confiscate it.
On their way to Concord, the British had to pass through Lexington. A patriot militia group awaited them there and a short skirmish broke out. The British marched on to Concord and encountered resistance there as well. As they marched back to Boston, they were subjected to constant attacks from patriot militias.
The war did not start right away after this battle. However, the fact that serious armed conflict had occurred made the war almost inevitable. Thus, these battles are significant simply because they represent the start of the war.