When a bowman shooteth an arrow, he may or may not succeed in slaying even a single person, but when an intelligent individual applieth his intelligence (viciously), it may destroy an entire kingdom with the king. Discriminating the two by means of the one, bring under thy subjection the three by means of four, and also conquering the five and knowing the six, and abstaining from the seven, be happy.
In plain words: An arrow may kill one person or none, but a clever mind used for evil can destroy a whole kingdom. Vidura then gives a riddle: use your mind to tell right from wrong, control the three (friend, enemy, neutral) with the four ways of influence, master the five senses, know the six strategies of statecraft, avoid the seven vices, and be happy.