When the time is short we must make the most of every opportunity and waste nothing. Ordinarily if we speak the Word to someone and they send us away, the best advice is to leave. Unfortunately, Paul was in prison and could not get away. Felix sent for him often but nothing ever changed. In this manner Paul witnessed to Felix for two years without any result whatsoever. Clearly this was a ruse of the enemy designed to frustrate the gifted apostle and sap his strength.
Paul the prisoner had no choice but to come when Felix called for him; we who are free ought to be careful lest we find ourselves spending all our time talking to a Felix when there is a Cornelius praying to hear us speak the very words that Felix takes for granted.