Although I do not know for certain what you are reading in this class, I will assume that your question refers to a speech that Benjamin Franklin gave to the Constitutional Convention. This speech was given on the final day of the convention, September 17, 1787. What we know of the speech today comes from notes that were taken by James Monroe. You can read the full text of the speech at this link.
In this speech, Franklin admits that he has his doubts about the Constitution. This is mostly, he says, because he doubts his own ability to know what is best. He says that he has lived long enough to find out that he can often be wrong when he thinks he is right.
Even though he has his doubts, he has three reasons why he has decided to accept the new document produced at the convention. First, he says that
I agree to this Constitution, with all its Faults, if they are such; because I think a General Government necessary for us…
When he says “a General Government,” he means a strong federal government. So, in our language, his first reason for accepting the Constitution is because he thinks the country needs a strong federal government.
Second, he says that
I doubt too whether any other Convention we can obtain, may be able to make a better Constitution…
He goes on to say that any meeting of a large number of people will inevitably make mistakes. People all have their own prejudices and their own wants and those will not always produce the right outcomes. However, Franklin says, the document this meeting has produced is as close to perfect as he thinks it could be. The second reason, then, is that Franklin thinks that it is unlikely that a convention could create anything with fewer problems than the Constitution has.
Finally, Franklin says
I hope therefore that for our own Sakes, as a Part of the People, and for the sake of our Posterity, we shall act heartily and unanimously in recommending this Constitution…
Here, again, he is saying that this is a document that will create a good government if people will administer it well. He is saying that it will be good for the people and for their posterity, which means their descendants. He accepts the Constitution because he believes it will be good for people in the present and in the future.
To sum up, then, we have three reasons why Franklin accepts the Constitution. First, he thinks a strong federal government is necessary. Second, he thinks that it would be impossible to make a constitution that is closer to being perfect than this one is. Finally, he thinks the Constitution will be good for people in his time and in the future.
If you're interested, here is an audio version of the speech: