What is the difference between an evil thought and the resolve to commit a sin?

The difference between a fleeting thought (hamm) and a firm resolve ('azm) is that 'azm is stronger than hamm. 'Azm is the settling of the soul upon doing something and striving earnestly to execute it, whereas hamm is merely the passing of an idea through the mind without the soul settling on the action or seeking to achieve it. One who firmly resolves upon a sin and settles his soul on it is sinful, but one who merely has a fleeting thought about it without it becoming settled is not sinful.