To put it simply, your house has a debt on it (mortgage) and I want to buy your house.
I get a mortgage to buy the house. I give you the money, you pay off the debt (mortgage) and keep whats left. My mortgage company put a charge on the title deeds of my house to protect their money.
However, we are not at the stage yet. We are at, I have looked at your house and want to buy it. I put in an offer to buy it and you say yes.
I now have to go away and get the mortgage company to front the money and they want to make sure they will get the money back i.e I can afford to pay the monies back.
In the above scenario though, what is missing, is the premier league are yet to ratify that 777 will pass the fit and proper persons test.