Paul uses "Today" from Psalms 95:7 in its broadest sense: the time we are called.
John W. Ritenbaugh
The Fourth Commandment (Part 4)
The will is the power or faculty by which the mind makes choices and acts to carry them out. At first, against his will, a person engages in some forbidden pleasure because he wants to, but if he keeps it up, he soon finds that he has no strength to resist it. This process does not happen any more quickly than an addiction to alcohol, but in the end, he keeps sinning because he cannot help but do so! Once a thought or act becomes a habit, it is a short step to being a necessity. The old saying is true: "Sow an act and reap a habit; sow a habit and reap a character; sow a character and reap a destiny."
Hebrews 3:12-13 reveals a worrisome characteristic of sin: "Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; but exhort one another daily, while it is called 'Today,' lest any of you be hardened through the deceitfulness of sin." Sin is seductive, enticing, deceitful, and hardening.
Sin's deceitfulness is that it cannot deliver what it promises. It deludes a person into thinking he can "have it all" or "take it or leave it." It promises pleasure, contentment, fulfillment, and life, but what it delivers in those areas is fleeting, which leads to its addictive quality. The pleasure is never quite enough to produce the desired contentment and fulfillment. Sinners are forced into greater perversions until it kills them.
Sin offers rationalizations and justifications. It puts on a plausible appearance and can even seem to be virtuous, as in situation ethics. However, sin's drug-like quality always demands more because what formerly satisfied no longer will. The person in its grip gradually becomes its slave, and all along the way, his heart becomes hardened as well.
In Hebrews 3:13, hardened is translated from the Greek word for a callus. A callus forms around the break in a bone, on the palms of hands and on fingers from constant hard use, or in a person's joints, paralyzing its actions. In a moral context, it suggests "impenetrable," "insensitive," "blind," or "unteachable." A hardened attitude is not a sudden aberration but a habitual state of mind that shows itself in inflexibility of thinking and insensitivity of conscience. It can eventually make repentance impossible.
Jeremiah 9:1-5 describes people in this state, so inured, so enslaved to sin that they weary themselves pursuing and doing it:
Oh, that my head were waters, and my eyes a fountain of tears, that I might weep day and night for the slain of the daughter of my people! Oh, that I had in the wilderness a lodging place for wayfaring men; that I might leave my people, and go from them! For they are all adulterers, an assembly of treacherous men. "And like their bow they have bent their tongues for lies. They are not valiant for the truth on the earth. For they proceed from evil to evil, and they do not know Me," says the LORD. "Everyone take heed to his neighbor, and do not trust any brother; for every brother will utterly supplant, and every neighbor will walk with slanderers. Everyone will deceive his neighbor, and will not speak the truth; they have taught their tongue to speak lies, and weary themselves to commit iniquity."
John W. Ritenbaugh
The Elements of Motivation (Part Seven): Fear of Judgment
We all need to guard against unbelief as we would against an enemy. Paul is not speaking about a heart in which unbelief is merely present, but a heart that is controlled by unbelief, the kind of heart that will drag a person down even as Peter was dragged down into Galilee's water when he took his eyes off of Jesus. The peril of unbelief is that it breaks the trust on which our relationship with God is based. Unbelief leads to falling away, which is the opposite of drawing near. "Drawing near" is a major theme of Hebrews.
Falling away is the supreme disaster of life, the ultimate defeat, because it completely thwarts God's purpose for creation. It is essential we remember that when a person falls away, he is not merely falling away from a doctrine or even a set of doctrines, but from a living, dynamic Personality.
Faith needs to be cultivated. It grows by reading and studying God's Word, and by meditating on it. It grows in an atmosphere of trial or experience because it is exercised through use. It also grows, as we find here in these three verses, in an atmosphere of exhortation from others who are fellowshipping with us. Exhortation is a preventative of falling away, which is a major reason why fellowship is so necessary. Without it, a person may hold his own, and perhaps his faith will not slip very much, but one who is not fellowshipping with others of like mind will rarely ever grow.
John W. Ritenbaugh
Faith and Prayer
"The deceitfulness of sin"! In this context, to be deceitful is to be seductively and enticingly misleading. Sin promises what it cannot deliver. It promises pleasure, contentment, fulfillment—life—but its delivery on these things is fleeting and ultimately unsatisfying. Its deceitfulness is the very reason why it has addictive qualities. It lures us on to try to capture what it can never deliver.
The pleasure is never quite enough to produce the contentment and fulfillment one desires. Thus, people are forced into greater and deeper perversions until it results in death. All along the way, from its inception to death, sin quietly produces hardness of heart. Like a callus that forms over a break in a bone or stiffens a person's joints, sin paralyzes right action.
"Hardness" is translated from skleruno, from which name for the disease multiple sclerosis is derived. In a moral context, it means "impenetrable," "insensitive," "blind," "unteachable." A hardened attitude is not a sudden aberration, but the product of a habitual state of mind that reveals itself in inflexibility of thinking and insensitivity of conscience. Eventually, it makes repentance impossible. The will to do right is completely gone.
The will is the power or faculty by which the mind makes choices and acts to carry them out. An old adage says: "Sow an act and reap a habit; sow a habit and reap a character; sow a character and reap a destiny." At first, against his will, a person engages in some forbidden pleasure out of weakness, curiosity, or sheer carnality. If the practice continues, he sins because he cannot help doing so; he is becoming addicted to it. Once a sin becomes a habit, he considers it to be almost a necessity. When it becomes a necessity, the destiny is produced.
John W. Ritenbaugh
What Sin Is & What Sin Does