"The just shall live by faith" is both a statement of fact about the basis of a Christian's life and a command. It is so important that it appears once in the Old Testament and three times in the New (Habakkuk 2:4; Romans 1:17; Galatians 3:11). In each case, the context is somewhat different, but its importance to a Christian's salvation is not lost.
The concept is not difficult to understand. Paul further clarifies it in II Corinthians 5:7: "For we walk by faith, and not by sight." A simple definition of faith in Webster's New World Dictionary is "complete trust, confidence, or reliance." At the end of the definitions, "belief" is listed as a synonym. Belief means "faith, esp. religious faith; trust or confidence." The dictionary definitions show that the two words are virtually synonymous. However, in the Bible and in practical application a very wide difference separates merely believing and living by faith.
The practical application of faith is more than simply acknowledging the reality of God. Living by faith involves qualities that are better expressed by the word "trust." This kind of faith produces loyalty or faithfulness expressed in the Christian's life by works of obedience.
Do you think for a moment that the Israelites in the wilderness disbelieved that God existed? Some few may have argued that the miracles they had experienced from the arrival of Moses in Egypt until they died in the wilderness were nothing more than natural phenomena. There are always some doubters and scoffers of that sort (II Peter 3:3-7).
But the vast majority of Israelites could not deny to themselves God's mighty acts on their behalf. They had heard the voice of God at Mount Sinai, had seen a wind from God part the Red Sea, and had escaped death on Passover while the Egyptian firstborn had died. But when God required a higher level of obedience to follow His cloud across the wilderness and depend on Him to supply their every need, the record shows they did not trust Him. Their loyalty dissolved, and they rebelled! They did not have it within them to live, or walk, by faith.