Ferguson spent the festive season raging at referees - first, laying into Michael Oliver for his performance in the 1-1 draw at Swansea and then confronting Mike Dean as United came from behind three times to beat Newcastle 4-3 on Boxing Day.
"When you see Sir Alex arguing with referees and linesmen, he is showing passion that has taken him to the very highest level of the game," Van der Sar told the Sunday Mirror.
"In a way, you are seeing Sir Alex at his very best. This is the passion he has always shown for his players and for the club.
"I saw him make his point often enough when I was playing for the boss at United, so I think I know him well. And everything that Sir Alex does is for a reason.
"When you see him arguing with the referee at half-time, like he did against Newcastle, he is hoping to create something that will change the game in the second half.
"He is purely doing it for the team because he stands up for his players. And, as player, I used to love that about him.
"I think every player gives a bit extra when he sees that his manager is fighting too. It really is a signal towards the players."