From the time you first start learning about U.S. government right on up to the highest levels of education, people never shut up about checks and balances. That's probably because they are kind of the bread and butter of the U.S. style government: a classic rock paper scissors countering system where everyone plays nice even when they hate each others' guts.

So it should come as no surprise that this same system was implemented in the Missouri Compromise. A series of checks and balances was necessary to make sure that no one party in the Compromise gained an excessive upper hand.

The Missouri residents were allowed to elect their representatives of choice, but from districts set up by Congress:

And be it further enacted, That the members of the convention thus duly elected, shall be, and they are hereby authorized to meet at the seat of government of said territory on the second Monday of the month of June next; and the said convention, when so assembled, shall have power and authority to adjourn to any other place in the said territory, which to them shall seem best for the convenient transaction of their business; and which convention, when so met, shall first determine by a majority of the whole number elected, whether it be, or be not, expedient at that time to form a constitution and state government for the people within the said territory, as included within the boundaries above designated; and if it be deemed expedient, the convention shall be, and hereby is, authorized to form a constitution and state government; or, if it be deemed more expedient, the said convention shall provide by ordinance for electing representatives to form a constitution or frame of government; which said representatives shall be chosen in such manner, and in such proportion as they shall designate; and shall meet at such time and place as shall be prescribed by the said ordinance; and shall then form for the people of said territory, within the boundaries aforesaid, a constitution and state government […] (4.1)

And these representatives could organize themselves as they saw fit, and draft the constitution of their choosing, but it would be subject to Congressional approval. In this way, the rights and powers of the state and federal government would balance each other out in order to forge the best path forward.

Unless you were a slave of course, in which case you got zip.