The question has been asked, "Can a person who has committed such atrocious crimes, and so long remains impenitent, be indeed a child of God, a member of Christ, a temple of the Holy Spirit, and an heir of everlasting glory? Can one spark of Divine life exist unextinguished, in such an ocean of evil?" Were we left to our own unaided judgment to make reply, most probably every last one of us would promptly answer—No, such a thing is unthinkable! Yet in the clear light of Holy Writ, it is plain that such things are possible. Later David made it manifest that he was a truly regenerated person, by the sincerity and depth of his contrition and confession. Yet, let it be said that no man while guilty of such sins, and before he genuinely repents of the same—can have any warrantable evidence to conclude that he is a believer; yes, everything points to the contrary. Though grace is not lost in such an awful case, Divine consolation and assurance is suspended.
But now the question arises, Why did God permit David to fall so low and sin so terribly?
The first answer must be, To display His high and awe-inspiring sovereignty. Here we approach ground which is indeed difficult for us to tread, even with unshodden feet. Nevertheless there is no doubt that there is a marvelous and sovereign display of the Lord's grace toward His people in this particular respect, both before their calling and after. Some of the elect are permitted to sin most grievously in their unconverted state, while others of them, even in their unregenerate days, are wondrously preserved. Again; some of the elect after their conversion have been Divinely allowed to awfully fall into the most horrible impieties, while others of them are so preserved as never to sin willfully against their consciences from the first conviction to the very close of their lives (Condensed from S.E. Pierce on Hosea 14:1).
This is a high mystery, which it would be most impious
for us to attempt to pry into: rather must we bow our heads before it and
say, "Even so, Father, for so it seems good in Your sight." It is a solemn
fact, from which there is no getting away, that some sin more before their
conversion, and some (especially those saved in early life) sin worse after
their conversion. It is also a plain fact that with some saints God most
manifests His restraining grace, and with others His pardoning
grace. Three things are to be steadily borne in mind, in connection with the
sins of the saints.
A second answer to the question, Why did God permit David to fall so fearfully, and sin so grievously? may be: that we might have set before our eyes the more clearly—the awful fact that "the heart is deceitful above all things, and desperately wicked" (Jer. 17:9). Unmistakably plain as is the meaning of those words, uttered by Him who cannot lie—yet how very slow we all are to really receive them at their face value, and acknowledge that they accurately describe the natural state of every human heart—that of the Man Christ Jesus alone excepted. But God has done more than make this bare statement: He has placed on record in His Word illustrations, exemplifications, demonstrations of its verity—notably so in allowing us to see the unspeakable wickedness that still remained in the heart of David!
Third, by allowing David to fall and sin as he did, God has graciously given a most solemn warning to believers in middle life—and elder Christians also. "Many conquerors have been ruined by their carelessness after a victory, and many have been spiritually wounded after great successes against sin. David was so—his great surprisal into sin was after a long profession, manifold experiences of the grace of God, and watchful keeping of himself from iniquity. And hence, in particular, has it come to pass—that the profession of many has declined in their old age or riper time: they have given over the work of mortifying sin—before their work was at an end. There is no way for us to pursue sin in its unsearchable habitation, but by being endless in our pursuit. The command God gives in Colossians 3:5 is as necessary for them to observe who are toward the end of their race, as those who are but at the beginning of it" (John Owen).
Fourth, the fearful fall of David made way for a display of the amazing grace of God, in recovering His fallen people. If we are slow to receive what Scripture teaches concerning the depravity of the human heart and the exceeding sinfulness of sin—we are equally slow to really believe what it reveals about the covenant-faithfulness of God, the efficacy of Christ's blood to cleanse the foulest stain from those for whom it was shed, and the superabounding grace of Him who is "the Father of mercies and the God of all comfort." Had David never sinned so grievously and sunken so low—he would have never known those infinite depths of mercy which there are in the heart of God!
Also, had his terrible sin, his subsequent broken-hearted confession, and his pardon by God, never been placed in the Divine record—not a few of God's people throughout the centuries would have sunk in abject despair.
Fifth, to furnish a fatal stumbling-block to blatant rebels. It is certain that thousands through succeeding generations have, by this fall of 'the man after God's own heart,' been prejudiced against true religion, hardened in infidelity—or emboldened in blasphemy; while others have thence taken occasion to commit habitual wickedness under a religious profession, and with presumptuous confidence, to the still greater discredit of the Gospel. It should, however, be considered, that all these have been, previously, either open enemies to true religion—or hypocritical pretenders to it: and it is the righteous purpose of God, that stumbling-blocks should be thrown in the way of such men, that they may 'stumble, and fall, and be snared, and taken, and perish.' It is His holy will, thus to detect the secret malignity of their hearts, and to make way for the display of His justice in their condemnation. On the other hand, thousands from age to age, have by this awful example of David's terrible sin, been rendered more suspicious of themselves, more watchful, more afraid of temptation, more dependent on the Lord, and more fervent in prayer; and by means of David's fall—have, themselves, been preserved from falling!