“As for his father, because he cruelly oppressed, spoiled his brother by violence, and did what is not good among the people, behold he will die in his iniquity.”
The grandson's goodness will not protect his father. His father will be brought to account for his sins. He will take responsibility for his own actions. Nor will the righteousness of his father save him. Everyone is finally individually accountable.
A Summary.
Note the positiveness of the whole passage. Had the prevailing position been totally in mind the contrast would have been between two wicked and one righteous. But the concentration is here on the blessing of the righteous, and the attitude is positive. The threefold generations may well have in mind the idea that Israel began well, sank into sin and now have the opportunity to repent resulting in full restoration.
Furthermore it does away with the fatalism of those who felt that they were at the mercy of their fathers' doings. Let them but arise and change and all will be different. Each man is responsible for his own sin and his own life, and finally determines his own destiny. The future can be rosy, but only if they go forward with their hand in the hand of God.
Ezekiel was not questioning the continuity of the effects of sin. The consequences of sin often go on long after the sin is forgiven, and sadly embrace others, often to the third and fourth generation. The life of David was constantly beset by the consequences of his forgiven sin, and he was finally refused the privilege of building the temple because of them. And his manner of life badly affected his sons. But Ezekiel is stressing final individual responsibility, and that God can compensate for a man's background, and will not hold it against him where he seeks to do the right.