posted by YASHNI .
what ia the dramatic importance of the passage ACT 1 SCENE 3 WHEN POLONIUS ENTERS?
That is not a passage. It is a stage command or "cue".
It is the scene in which Polonius' oft-quoted "advice to Laertes" speech occurs. They both play an important part in the story line.
I think it set the social conflict for the rest of the play: that which is rotten in Denmark. The choice is what the brother says, and the father says: truth vs nonsense maxims. The truth is that Hamlet will love just as much as Denmark allows, no more, and that is what is rotten in Denmark.
It's also setting up the parallel plot -- Hamlet avenging his dad's death = main plot; Laertes avenging his dad's death = secondary (parallel) plot.
Parallel plots are included to set up "foils" for the main plot -- here, to contrast how Laertes reacts (immediately and violently) to how Hamlet reacts (hem-hawing around, avoiding making a decision and acting on it...).