In this period of time there were essentially two sides that either believed it the constitution should be ratified or that it wouldn't be ratified (These two groups referred to themselves as the federalist and anti-federalist). There were many arguments over what some may call a small problem, but really this small thing is what molded the country as a whole.
Now the first reason that the federalist brought up was that, this constitution would bring together the states as a whole which would then create a strong central government.
Not only that, but they had also said that with this constitution it would also fix the weaknesses in the almost established country. These weaknesses in a big picture sense don't seem very problematic, but to the federalist, who were very dedicated, thought these issues needed to be fixed for a stronger central government.
Finally, the last reason the federalist brought up was the problem with citizens being threatened by a strong government while also having to risk the rights they had already fought for. Then once addressing this they then brought out that the power given to the government would be limited and with this there would be three separate branches.
The three branches can be shown here which are the legislative, executive, and the judicial branches. These branches had an equal divided power so that the government wouldn't seem threatening.