Single combat is a duel between two warriors who each represent their side. It might be too costly for each side to engage in full scale warfare, so each side would send their champion. God promised to send a champion–his Son. He went toe to toe with Satan and he did what we could not. In meeting and defeating Satan our champion gives us the victory we need.
What do you really need right now? If you lack something you want, life goes on just fine. If you lack something you need, that presents a problem. So, to answer the question you must understand your greatest problems. We do not look at our problems to despair, but so a solution can be applied to them. The solution in Christ. In Christ, all our greatest needs are met.