Landlord Tenant issue in US

[SOGVET7]

I'm a father of 3 with a wife in ill health. After one year of renting I agreed to a month to month lease with our landlord. Only a month ago he asked me to furnish him with a letter for his bank stating that my wife and I would agree to staying 9 to 10 months barring any unforseen circumstances on our part - job relocation, natural disaster etc. My wife and I both signed this and sent it to him - I made a copy and the day I sent it. My landlord said he recevied it. My landlord and I have had a very good relationship. I even have a document he sent me saying so but he also stated he want to start showing the house b/c he wants to sell it. My wife and I said that we wanted the 9 to 10 months to get our finances together and look at buying a home just not this one. He wants to show the house and we have already said no not on that day. We don't want to have to show the house on 24 hours notice with my wife's condition nor have to move sooner than we are ready. Does the letter he asked for hold any merit that would help us point to the fact that he wanted reassurace that we were going to stay for the next 9 - 10 months?