It may well be that the Lord is not referring here to their “evil thoughts”, but to that they thought that “evil thing”, namely, blasphemy was happening in front of them. Thus, the sentence can be rendered as such: “Why do you think of evil [happening before you], for, as you will be immediately shown, nothing evil or blasphemous is there in my words”.

It may well be that the Lord is not referring here to their “evil thoughts”, but to that they thought that “evil thing”, namely, blasphemy was happening in front of them. 

Thus, the sentence can be rendered as such: “Why do you think of evil [happening before you], for, as you will be immediately shown, nothing evil or blasphemous is there in my words, because I share the dignity and authority with Him who is the only one authorized to forgive sins - God; that you may know it, I shall show it to you by healing a visible infirmity without prayers, by my own sovereign authority, and through this fact you will be assured that when I say that I have healed the guy's soul's invisible infirmity (for to forgive sins means nothing else than healing the inner, invisible infirmity of man's soul) I was not saying a lie, but I meant it have happened through my divine action”.