Are we content with merely hearing the Word of God? Perhaps, to a certain degree, we should admit, if not strive for, contentment upon solely hearing His Word. For, the divine speech is always a reminder that an all-holy God initiates a loving, communicative relationship with His creation, overcoming our sinful predicament and separation from Him; He condescends to us, speaking to us according to the rules of our language, so that we might be transformed, sanctified, and endowed with an understanding of His. But, if contentment means that when we only "hear" we are there satisfied, not to be led unto transformation, then we have not truly heard. This type of hearing is not the "one thing [that] is necessary" which Mary chose (see Luke 10:38-42). For, when it comes to the living Word of God, the type of hearing that goes no further has only registered an auditory response, instead of allowing the divine speech to run its proper course and penetrate to the depths of the body, mind, and soul. As this passage in Hebrews reminds us, we have not genuinely heard the words of God until it is "united by faith" (Hebrews 4:2). This combination (hearing + faith) results in "profit," because it results in transformation, obedience in love, and a desire to be drawn into the eternal Person whose living words bring us sweet relief and entrance into rest.
In the last chapter, we saw that the writer of Hebrews unites (to some degree or other) the concept of belief with obedience, and unbelief with disobedience. So, for example, the chapter ends by conjoining the second of these pairs:
And to whom did He swear that they would not enter His rest, but to those who were disobedient? So we see that they were not able to enter because of unbelief. (Hebrews 3:18-19, emphasis added)
That is, God disallowed entrance for those who were "disobedient" (v. 18), but the inability to enter was also predicated upon their "unbelief" (v. 19). With this in mind, the author introduces a third related concept that will reappear later in this epistle as a rather significant theme, that of "faith" (4:2). And, as we might expect, possessing faith is akin to belief and obedience, while lacking faith corresponds to unbelief and disobedience.
Now, I don't want to give the false impression that each of these terms (faith, belief, obedience) and their negative counterparts (lack of faith/faithlessness, unbelief, disobedience) are purely synonymous. Still, depending upon our own unique preconceptions and contemporary understanding(s) of these, we may or may not be surprised that they must have at least some degree of overlap in their meanings, which, for the epistle to the Hebrews (and other NT books), makes their use at times interchangeable. Consider the following points derived from the example of the Israelites in the wilderness:
If we hear the voice of the Holy Spirit, we are not to harden our hearts as did those in the wilderness (3:7-8)
Those who did harden their hearts went "astray in their hearts" and "did not know [God's] ways" (i.e., they disbelieved and were disobedient) (3:10)
Those who disbelieved and disobeyed aroused God's anger and did not enter His rest (3:11)
God swore that those who were "disobedient" that they would not enter His rest (3:18)
But, they were not able to enter because of "unbelief" (3:19)
And, "they failed to enter because of "disobedience" (4:6)
With their example in mind, we are to "take care" that we don't have "an unbelieving heart" that causes us to "fall away" (3:12)
Also, their example cautions us against following the same "disobedience" (4:11)
Those in the wilderness "heard" the Holy Spirit's words, but their hearing was not "united in faith" (4:2)
In contrast to the "disobedien[ce]" (3:18) and "unbelief" (3:19) among those who did not enter because "hear[ing]" was not "united with faith" (4:2), those "who have believed" do "enter" into God's rest (4:3)
Again, if I am being redundant, it is for the purpose of inculcating a simple truth: faith and belief and obedience are perhaps more intimately wed than we are accustomed to consider. It is all too easy in, for example, a systematic approach to theology (which I am not against), that we engender a tendency to construct rigid, separatist conceptual boundaries around notions whose boundaries actually overlap. This is further problematized if we are not careful with the manner in which we define concepts and terms. So, one very helpful way to define something is to say what it is not. But, if we assume lacking relationships among concepts such as "faith," "belief," and "obedience" then we may incidentally define these in a manner such as "faith, whatever it is, is not in any way belief and is not in any way obedience," or "belief, whatever it is, is not in any way obedience and it is not in any way faith." Though this can method can be initially helpful in our understanding, we can take it too far and create strong conceptual divisions that are not intended by the biblical authors themselves. One of the salient features of these passages in Hebrews, then, with regard to faith and belief and obedience (and their opposites), is that (in a biblical framework) we cannot pretend to possess one without the other if indeed we desire to actually enter into the rest that God has both promised and invited us to enter into. As I cautioned above, these are not completely synonymous, and we do have a burden to make explicit the way(s) in which they correspond to each other. But, despite this, it is clear that the writer of Hebrews wished that the primary audience (and now to us by extension) understand the relatedness of these concepts and how they factor in to our ability to enter or not enter into God's rest.
From this portion of Hebrews, there are at least two significant reasons why any Christian should see the relatedness of these concepts as important. First, we are in some sense just as susceptible to "falling away" as were the Israelites in the wilderness. For this reason, Hebrews encourages us to "fear" so that we do not in any way "come short of" the promise to enter into God's rest, which is still available through Jesus Christ. It is not sufficient to say that we have merely heard the "good news," because hearing is ineffective unless it is "united by faith" (4:2). The content of the Good News is made more explicit now that Christ has come, but the action of hearing can be done by believers and nonbelievers alike. Only those that believe have, by God's grace, united faith with hearing, which is evidence that we believe the Gospel with utter conviction of its truth - and this faith and belief leads to obedience in love. Conviction is not genuine if, when provided the opportunity, it does not lead to action. The one who hears and believes in faith evidences a holy desire to do the will of God because they are constrained by the love and strength that He provides while perpetually trusting in Him and being sustained by Him. Second, if (and only if) we "have believed" (in the biblical sense), we do enter into God's rest (4:3), even though we have a call to "be diligent to enter that rest" (4:11). For the one who believes toward obedience, whose hearing is united by faith, there is a present experience of God's rest that is not diminished, but rather completed and augmented by the future reality when we will know Him just as we are known (1 Corinthians 13:12). While we must take care to understand the differences between faith, belief and obedience, we also ought to give proper priority to their relatedness, so that we can truly enter into the Sabbath rest that God has promised to those who love Him (see James 1:12; 2:5).