Blake was already "getting a move on," and he needed no such spur as the Old Man's letter.

But the letter did the Old Man a lot of good, so that it served its purpose.
Blake had no intention of handling the case from the Flying U porch, for instance.

He had laid his plans quite independently of the Flying U outfit.

He had no intention of letting Irish be arrested upon a trumped up charge, and he managed to send a word of warning to that hot-headed young man not to put himself in the way of any groping arm of the law; it was so much simpler than arrest and preliminary trial and bail, and all that.

He had sent word to Weary to come and see him, before ever he received the Old Man's letter, and he had placed at Weary's disposal what funds would be needed for the immediate plans of the Happy Family.
He had attended in person to the hauling of the fence material to their boundary line on the day he arrived and discovered by sheer accident that the stuff was still in the warehouse of the general store.
After he did all that, the Honorable Blake received the Old Man's letter, read it through slowly and afterwards stroked down his Vandyke beard and laughed quietly to himself.