Scripture quite clearly teaches that God is immutable. This means he does not change, have mood swings, or go back on something he said. God is the constant one. James 1:17 says there is no change or shadow of turning with God. Malachi 3:6 says, “I am the LORD, and I do not change” (NLT). The Psalmist puts it this way in a prayer to the Lord: “You are always the same” (Ps. 102:25 NLT). The doctrine of God’s immutability is a truth that brings much comfort to the Christian’s heart, mind, and soul. Here’s how Petrus Van Mastricht applied the doctrine of God’s immutability:
“For this reason he is called the rock (Deut. 32:31; Ps. 73:26) upon which the church has been built (Matt. 16:18). For if the godly are vexed, perhaps in regard to their eternal salvation, because of the inconstancy of their own heart, together with the immutable treacheries of their spiritual enemies, what will sustain them more effectively than the fact that their immutable God (Ma. 3:6) is a rock and unmoved builder, whose firm foundation stands, by which the Lord knows those who are his (2 Tim. 2:19), whose saving gifts are without repentance (Rom. 11:29)?
Or if they are vexed about the vicissitudes of temporal things, whether the stirrings of war, diseases, or whatever other calamities, what will more effectively comfort them than to consider that
1) the immutability of the one God is a law fixed in their favor, and that all other things are only immutable in their motion and flux (1 Cor. 7:29).
At the same time that 2) God, through all these motions and vicissitudes, will be present, unmoved, for the sake of his own (Ps. 46:1-7), present in his perfection and strength, that they may not be shaken (Ps. 90:1).
That 3) he is immutable in goodness, love, grace, and mercy (Is. 54:10; Ps. 117:2; 118:1, 2, 5),
and also 4) in his will and gracious decrees by which he knows his own (2 Tim. 2:19; Heb. 6:17-18),
and in addition, 5) in his promises, so many and so great (Num. 23:19), all of which will be yes and amen in Christ (2 Cor. 1:20; Heb. 13:15), and especially in his faithfulness and covenant (Is. 53:3; 54:10; Hos. 2:19).
What could be more effective for our consolation than all these things?
Petrus Van Mastricht, Theoretical-Practical Theology, vol. 2. p. 162.
Covenant Presbyterian Church (OPC)
Hammond, WI, 54002