In this scene, the ghost appears to Hamlet and beckons him to follow it. Hamlet wants to go but he is counseled against it. Marcellus and Horatio attempt to stop Hamlet from following the ghost. Just before the quoted line, we see them trying to physically hold him back. Hamlet is threatening to kill them for stopping him. We see that Hamlet is so determined to follow the ghost, he would take revenge, even on his own friends, for preventing him. Revenge simply means to get back at someone for a perceived injustice. Hamlet believes his friends are wrong to hold him back. He will get back at them, or have his revenge, if they prevent him from doing what he wants to do.