Preamble an improvement over the opening sentences of the Articles of Confederation.
The opening statement of the Constitution is Preamble which gives an insight into the minds of the Drafters of the Constitution as to why they chose Republic form of government. Preamble has substituted the Articles of Confederation.
Preamble is certainly an improvement over the opening words of the Articles of Confederation in form as well as content. If we talk about form, the preamble is concise, shorter and conveys its goals clearly and with regards to content it defines American nation as one single entity which is created not by the States but by the people of America.