The most significant aspect of the Declaration of Independence is that it was used to define the relationship between people and government. The document articulated the principles of individual rights and government accountability, asserting that governments are derived from the consent of the governed and that people have the right to alter or abolish any government that becomes destructive to these ends. This foundational concept has had a lasting impact on democratic thought and practice.
The other options are not accurate: the declaration did not establish the importance of government power itself, it did not immediately end the war with Britain (the war continued until the Treaty of Paris in 1783), and while it had its critiques, it isn't accurate to say it was completely avoided due to flaws.