When you rent it out, will the rent be less than or equal to the sum of the depreciation of the property and the maintenance? And about the taxes: you pay taxes for the property that are intended to make up for the value the property is gaining to limit the rate at which landlords' wealth grows. If it doesn't gain value then you can run the numbers again allowing yourself to pass down the taxes to the tenants.

If not, you will be making a profit. That surplus amount corresponds to no actual value. The tenants would be paying for nothing, and you'd be getting money for doing nothing.

Whether that's theft or not depends on your definition of theft. I personally subscribe to the idea that if someone get an euro that they didn't work for, that's an euro someone else worked for and didn't get to keep. I don't believe this situation to be different from if you were to buy a stake in your local grocery chain which is making money out of putting commodities on the market which have in them the objectified human labor of everyone in the supply chain, and paying those people less for their labor power than what it's worth. The common term for that is "exploitation."

I also don't mean to make this a moral judgment. I don't know if you're gonna go to heaven or not, that's really not the crux of the issue here. I'm trying to give you an analysis of the economic forces at play, and if you ask me, the solution to the problem isn't for individuals to change how they behave on an individual level, it's for the working class to seize political power and abolish private property. But being a landlord aligns your class interest with the class that would prefer to keep the status quo.