The God of Scripture is the one true constant in all the universe: “I, the Lord, do not change” (Malachi 3:6). His nature and His thoughts are as immutable as His eternal plans. Specifically, He does not alter His Word, revise His will, revoke His promises, or change His mind: “God is not man, that He should lie, nor a son of man, that He should repent; has He said, and will He not do it? Or has He spoken, and will He not make it good?” (Numbers 23:19).
The necessary implication of God’s immutability is that He is not subject to shifting moods, flashes of temper, fluctuating dispositions, or seasons of despondency. In theological terms, God is impassible. That means He cannot be moved by involuntary emotions, suffering, pain, or injury. In the words of the Westminster Confession of Faith (2.1), God is “infinite in being and perfection, a most pure spirit, invisible, without body, parts, or passions.”
Divine impassibility is not an easy concept to grasp. Robert Ingersoll, the famous nineteenth-century skeptic, wrote, “Think of that!—without body, parts, or passions. I defy any man in the world to write a better description of nothing. You cannot conceive of a finer word-painting of a vacuum than ‘without body, parts, or passions.’”  Robert G. Ingersoll, The Works of Robert G. Ingersoll, 12 vols. (New York: Dresden, 1900) 2:361-62. Nowadays even some Christian theologians shun the idea of divine impassibility because they think it makes God seem cold and aloof.
But that’s a false notion. To say that God is not vulnerable, that He Himself cannot be hurt, and that He isn’t given to moodiness is not to say He is utterly unfeeling or devoid of affections. On the contrary, Scripture says “God is love” (1 John 4:8). His compassion, His lovingkindness, and His tender mercies endure forever (Psalm 136). His divine affections are more real, more sure, and more trustworthy than any human emotions could ever be. In fact, the constancy and infinity of God’s tender affections epitomize why divine impassibility is such a wonderful truth. “The Lord’s lovingkindnesses indeed never cease, for His compassions never fail. They are new every morning; great is [His] faithfulness” (Lamentations 3:22-23).
The main problem in our thinking about these things is that we tend to reduce God’s attributes to human terms, and we shouldn’t. We’re not to imagine that God is like us (Psalm 50:21). His affections, unlike human emotions, are not involuntary reflexes, spasms of temper, paroxysms of good and bad humor, or conflicted states of mind. He is as deliberate and as faithful in His lovingkindness as He is perfect and incorruptible in His holiness.
The unchangeableness of God’s affections is—or should be—a steady comfort to true believers. His love for us is infinite and unshakable. “As high as the heavens are above the earth, so great is His lovingkindness toward those who fear Him” (Psalm 103:11). And His constant mercy is a secure and dependable anchor—both when we sin and when we suffer unjustly. “As a father has compassion on his children, so the Lord has compassion on those who fear him” (Psalm 103:13). Far from portraying God as unsympathetic and untouched by our suffering, Scripture stresses His deep and devoted compassion virtually every time it mentions the unchangeableness of God.
Notice that I have quoted almost entirely from Old Testament texts to establish the connection between God’s compassion and His immutability. The commonly-held notion that the Hebrew Scriptures portray God as a stern judge whose verdicts are always unrelentingly severe is an unwarranted caricature. The tender mercies of God are a persistent theme throughout the Old Testament. From beginning to end the entire Bible presents God as “gracious and merciful; slow to anger and great in lovingkindness . . . good to all, and His mercies are over all His works” (Psalm 145:8-9).
In fact, God’s lovingkindness is often given particular stress in the very places where His fiery wrath against sin is mentioned. (See, for example, Nehemiah 9:17; Psalm 77:7-10; Isaiah 54:8; 60:10; Habakkuk 3:2). Even the prophets’ most severe threats and harshest words of condemnation are tempered with reminders of God’s inexhaustible kindness and sympathetic mercy (Jeremiah 33:5-11; Hosea 14:4-9).
Of course, there’s a careful balance that must be maintained here. It is neither wise nor helpful to pit the divine attributes against one another as if they were contradictory (they are not)—or to act as if God’s merciful attributes automatically overruled the gravity of divine justice (they do not). “Behold then the kindness and severity of God” (Romans 11:22). All God’s attributes are equally—and infinitely—exalted in Scripture.
It is a serious mistake to imagine that God’s wrath conflicts with His mercy. It is a particularly egregious error to pit God’s holiness against His tenderness or to think God's lovingkindness toward sinners simply cancels out His wrath against sin. Don’t dream for a moment that divine mercy eliminates the threat of God’s judgment. God would be unjust if He did not punish evildoers (Exodus 34:7; Nahum 1:3). On the contrary, God’s wrath magnifies His mercy—revealing the severity of punishment that we have been spared from.
There is no conflict or contradiction among God’s attributes. God’s unchanging nature doesn’t make Him incapable of responding to us with compassion. Rather, His impassibility reassures us that His compassion never changes.
(Some of the above material will be included in a book scheduled to be released by Ligonier Ministries in late 2016.)