Let's just say (and this is worst case scenario for Norway, other than the nightmare of not actually beating Estonia) that Norway beat Estonia 1-0 and Italy beat both Israel and Moldova 5-0 (I think realistically Norway will win by more and Italy will not rack up that many goals, but bear with me). That would put Norway's goal difference on +28 and Italy's on +17 - meaning Italy would need to beat Norway in the final game and there would have be a 12 goal swing i.e Italy winning by 6 clear goals. And this is the worst case scenario for Norway - assuming they win marginally and Italy rack up the goals in their final three games. They'd both finish on identical points - won 7 games and lose the away game to each other.
So, yeah, a win over Estonia by any margin and Norway are 99.99 percent qualified. They have already done the hard work building their goal difference. What
@ThwiX has said is right - Haaland is like Ronaldo, a falt-track bully who beats up on poor teams in qualifiers, which is perfect when the tiebreaker is goal difference (though to be fair even if the tiebreaker was head to head, they beat Italy 3-0 in the home game).
Hence, beat Estonia, and we will be seeing Norway at their first World Cup since 1998.