What is fascinating about this scene is the way that we are presented with a very different side to Polonius from what we have seen before. Note the way that prior to this scene, he has ostensibly given his every blessing to his son, Laertes, to return to his studies. In Act I scene 3, for example, after a series of bits of advice that he gives to Laertes, he ends up by saying:
Farewell: my blessing season this in thee.
He is to all intents and purposes presented as a loving father who wants the best for his son and trusts him to be able to manage his own affairs indepdendently.
However, Act II scene 1 immediately undercuts such an impression, as we realise that Polonius is hiring Reynaldo to keep an eye on Laertes and report back to Polonius concerning the character of Laertes and his various vices. We therefore see that Polonius is hypocritical by nature. He refuses to trust his son and give him his independence, not willing to relinquish his position of power over him.