Even if you hear others mention the name of a tzaddik, speak up; that’s what Mishlei tells us. Everyone knows that זֵכֶר צַדִּיק לִבְרָכָה – the memory of a tzaddik is for a blessing. (Mishlei 10:7). Now, Mishlei is not telling us a command here; he’s telling us a fact – Hakadosh Baruch Hu will see to it that when a tzaddik is remembered he will be acclaimed for his good deeds. That’s a promise from Hashem: “a man who lived for Me, I’ll make sure to it that he’s remembered l’vrachah.”
Now, that’s the poshut pshat but it’s not everything. Because the Gemara learns from this one step further – “If someone mentions the name of a tzaddik and he doesn’t bless him, he’s oiver the asei of zecher tzaddik l’vrachah” (Bereishis Rabbah 49).
It means that we don’t sit back and wait for Hakadosh Baruch Hu to do it; if He’s going to bless the memory of a tzaddik, then we should do the same. If it’s His will then let us do it all the way. That's why when you mention a tzaddik who's departed we say zal or zatzal. It's a command. זֵכֶר צַדִּיק – When a tzaddik is mentioned, לִבְרָכָה – make it your business to bless him.
But it doesn’t mean that you should wait until he dies. Yes, that too; even after he’s gone we should bless him when we mention him. But when he’s living, absolutely you have to bless him and praise him. It means if you mention the name of a tzaddik or even if someone else does, don’t let that opportunity go by. If a tzaddik's name is mentioned, say “Ah! What a man he is. What a glorious personality.’ Speak about it.
That’s the mitzvah of וְהִצְדִּיקוּ אֶת הַצַּדִּיק. When a tzaddik is spoken about in this world, a living tzaddik, it’s a mitzvah to declare his righteousness, to look for ways and means of speaking good about him.
