San Miniato would be but a poor thing in those great hands of Ruggiero's, though he was a well grown man and still young and certainly stronger than the average of fine gentlemen.
Of course it was a great sin to kill San Miniato.

Murder was always a sin, and people who did murder and died unabsolved always went straight into eternal fire.

But the eternal fire did not impress Ruggiero much.
In the first place Beatrice would be free and quite happy on earth, and in the natural course of things would go to Heaven afterwards, since she could have no part whatever in San Miniato's destruction.

Secondly, San Miniato would be with Ruggiero in the flames, and throughout all eternity Ruggiero would have the undying satisfaction of having brought him there without any one's help.

That would pay for any amount of burning, in the simple and uncompromising view of the future state which he took.
So he sat on the block of stone and listened to the sea and thought it all over quietly, feeling very happy and proud, since he was to be the means of saving the woman he loved.