I have a quaint memory from my younger days of a certain bar sign displayed in a restaurant that my family ate at every once and a while. Albeit, this may seem strange for a "childhood memory," but, nevertheless I'll proceed with the description: this sign hooked its viewer with the enticing phrase "Free beer tomorrow" prominently displayed in large, bold lettering. What was the catch? Just a minor caveat detailed in the fine print towards the bottom: "Tomorrow never comes." Now, this is, of course, no starting point for developing a robust philosophy of time, but it still resonates with me regarding the subtle deceptiveness of supposed future expectations and fulfillments. This last statement needs qualification; it should not be taken as though the future holds nothing for which we might long, and this is especially the case for the believer in Christ. For, the imminent, but (from our perspective) still future prospect of His glorious return provides the Christian with an unparalleled sense of hope at the thought of being united with Him in an even fuller sense than we now know, that of seeing Jesus "just as He is" (1 John 3:2). We have great and enduring hope in Him who we will soon see "face to face" with utter lucidity, and not as in a "dim mirror" (1 Corinthians 13:12). And, assuredly, "this hope we have as an anchor of the soul, a hope both sure and steadfast and one which enters within the veil, where Jesus has entered as a forerunner for us" (Hebrews 6:19-20a).
But this is in no way what I have in mind by invoking "supposed future expectations and fulfillments." The assuredness of Christ's future return and our being gathered together with Him (in perfect fulfillment of His High Priestly prayer [see John 17, especially verse 21]) are not merely "supposed," they are grounded in Christ's eternal faithfulness, which He can never deny as it would be a denial of His eternal Self (2 Timothy 2:13). The type of expectations to which I am referring are not so grounded, for they are ultimately based in a false sense of reality. That is, often we hold ourselves as principally sovereign individuals in control over our own "destiny." As such, we feel we have more or less a "right" of individual self-determination, including, say, putting off certain decisions under the pretense that we can in some way validly enact a guarantee of the future. If we were to carefully consider our own lives, I'm sure that we would discover that the tendency to delay some particular action - the attitude of "I'll get to it on the dawn of the evasive tomorrow" - hauntingly pervades much of what we fail to do. Fortunately, most of these instances we would find to be rather mundane and, taken individually and in isolation, to be of little or no consequence (except as it might pertain to our character). But, What is the consequence of applying this mindset toward weightier matters? What is the consequence of applying this mindset toward perhaps the weightiest matter that pertains to us as individuals - the response of a believing heart that falls into the hands of the living God?
This mindset that I speak of is at the root of those that harden their hearts against God and do not hear the Holy Spirit's invitation to hear God's voice today. This mindset evidences an attitude of unbelief and disobedience (see Hebrews 3:7-19). This is the mindset which the epistle to the Hebrews urges its original readership, and urges us today, not to participate in. Why is it so dangerous? Primarily, because it deafens us to hearing and accepting the purposes for which God has created us; it numbs us to the ability to, by God's grace, be a part of Christ's "house' (3:6). One striking feature of this particular verse is the content of its conditional nature. We ought to note carefully that it reads, "if you hear," and not "if He speaks." The implication, which accords with the reality, is that, God the Holy Spirit has already spoken and continues to speak today. We are strangely quick to admit that we would believe or obey God if He were to speak, but we do this to the betrayal of our consciences. Furthermore, we do this to the explicit denial of God and His Self-revelation. This is why failure to "hear" in Hebrews 3 is equated to a hardening of the heart. Here it is important to recall that the primary audience are already believers in Christ. Therefore, it is not due to an inability to hear that the heart is hardened, it is rather a direct refusal that makes the whole of our being callous to the voice of God. Still, He speaks, He reveals, He beckons, He draws; and all while it is still called "Today" (3:13).
Somewhat recently, I heard a sermon from Pastor Alistair Begg who mentioned the following rather astute observation:
"The devil's favorite word is 'tomorrow'; the Bible's exhortation is always 'today'" (Begg 2010)
Additionally, C. S. Lewis expands on this notion (though in a completely different manner) by communicating the idea of the devil's desire that we should idolize the future so that we may forget the present:
To be sure, the Enemy wants men to think of the Future too - just so much as is necessary for now planning the acts of justice or charity which will probably be their duty tomorrow. The duty of planning the morrow's work is today's duty; though its material is borrowed from the future, the duty, like all duties, is in the Present. This is not straw splitting. He [that is, Christ] does not want men to give the Future their hearts, to place their treasure in it. We do. His ideal is a man who, having worked all day for the good of his posterity (if that is his vocation), washes his mind of the whole subject, commits the issue to Heaven, and returns at once to the patience or gratitude demanded by the moment that is passing over him. But we want a man hag-ridden by the Future - haunted by visions of an imminent heaven or hell upon earth - ready to break the Enemy's commands in the present if by so doing we make him think he can attain the one or avert the other - dependent for his faith on the success or failure of schemes whose end he will not live to see. We want a whole race perpetually pursuit of the rainbow's end, never honest, nor kind, nor happy now, but always using as mere fuel wherewith to heap the altar of the future every real gift which is offered them in the Present. (Lewis 1943:78-79)
Thus, we must remember that we have an adversary that is all too willing (and wanting and waiting) to perpetuate our propensity to wait. The devil wishes us to be so enraptured by the future because, if we are, it will draw us away from that which God has presently given to us, including the words that He speaks. The devil wants us to begrudge the elusive nature of "today" (for it will not always be called such) so that we become fixated upon a future that overlooks what God has given to experience and obey now. But, God is stronger, and it is of great encouragement to remember that "greater is He who is in you than he who is in the world" (1 John 4:4). Despite this elusive nature of "today," which will soon become yesterday, it is (at present) the very temporal vehicle through which we experience God's presence and promises, and through which we respond in obedience by grace through faith. When it comes to calling of God in our lives that we, by His strength, remain faithful to the end, the stakes are too high to give in to the weak tempter whom Christ has already definitively defeated and made an open spectacle through His victorious cross. We have no overbearing burden to seek and grope after God in the dark; He has shined His glorious light and illuminated our hearts (John 1:4-5). He has revealed Himself, and He has indeed spoken. Even the temporal reality itself that presently bears upon us all urges us to respond to the loving God who is there and is not silent. Today, we must make a decision; then, we will rest in the faithfulness of God, who has and does keep us, in the eternal day without evening which is to come.
 For those who have not read Lewis' The Screwtape Letters, it is crucial to note here that he is writing from the perspective of a demon/devil named Screwtape training his nephew, Wormwood. In this unique context, then, "the Enemy" refers to Christ (as the enemy from Satan's perspective).
Begg, Alistair. (2010). Who Do You Say that I Am?, Part A. (ID# 0117). Aired on July 20, 2010.
Lewis, C. S. (1943). The Screwtape Letters. New York: NY, The MacMillan Company.