It is true that when the conflict becomes inevitable, we have to contend against all enemies, but a better tactic may sometimes be, to clean the surroundings first and get rid of the nearer enemy; and then proceed to the next groups who are farther. Of course there are exceptions in everything. The odds are that the farther enemy might be more dangerous than the nearer. In such cases we may attend to the farther, or even contend against both parties simultaneously, and in the same rush.
The second order in this verse is that the believers should show up a staut and stiff resistance to the infidel enemy. This is because the unbelievers are not spiritually a firm people in dangerous incidents. They are a compound of cowardice, greed, timidity and ignobility; and when they find their interests, and in particular their life in danger they leave every one and everything in order to save themselves.