In Act 2, Scene 1, the First Lord tells Duke Senior how he and the Lord of Amiens, along with Jacques, had seen a wounded deer come to the brook near them and stand "at the extremest verge of the swift brook / Augmenting it with tears." That is, adding water to the brook by dropping tears into it. When the Duke immediately asks, "But what said Jacques? Did he not moralize this spectacle?" he is obviously referring to the spectacle presented by the First Lord's long description of the "poor sequestered stag / That from the hunter's aim had ta'en a hurt..." The First Lord answers the Duke's question in another long speech in which he recounts the various ways in which Jacques did in fact moralize on the spectacle of the wounded deer, including the moral that the Duke and his followers "...Are mere usurpers, tyrants, and what's worse, / To fright the animals and to kill them up / In their assigned and native dwelling place."
spectacle means sight(sight of jaques)