unchangeable

Today's attribute of God is His unchangeableness (or immutability). God is unchanging in his being, perfections, purposes, and promises, yet God does act and feel emotions, and he acts and feels differently in response to different situations.

Psalm 102 contrasts things that we may think to be permanent such as the earth or the heavens to God.

Of old you laid the foundation of the earth,
and the heavens are the work of your hands.
They will perish, but you endure;
they will all wear out like a garment.
You change them like raiment, and they pass away;
but you are the same, and your years have no end.
(Ps. 102:25–27)

Again Wayne Grudem sheds some good light on the topic (Systematic theology : An introduction to biblical doctrine, p163) [emphasis mine].

God existed before the heavens and earth were made, and he will exist long after they have been destroyed. God causes the universe to change, but in contrast to this change he is “the same.”

Referring to his own qualities of patience, long-suffering, and mercy, God says, “For I the Lord do not change; therefore you, O sons of Jacob, are not consumed” (Mal. 3:6). Here God uses a general statement of his unchangeableness to refer to some specific ways in which he does not change.

James reminds his readers that all good gifts come ultimately from God “with whom there is no variation or shadow due to change” (James 1:17). His argument is that since good gifts have always come from God, we can be confident that only good gifts will come from him in the future, because his character never changes in the slightest degree.

The definition given above specifies that God is unchanging—not in every way that we might imagine, but only in ways that Scripture itself affirms. The Scripture passages already cited refer either to God’s own being or to some attribute of his character. From these we can conclude that God is unchanging, at least with respect to his “being,” and with respect to his “perfections” (that is, his attributes or the various aspects of his character).

The great Dutch theologian Herman Bavinck notes that the fact that God is unchanging in his being is of the utmost importance for maintaining the Creator/creature distinction, and for our worship of God:

The doctrine of God’s immutability is of the highest significance for religion. The contrast between being and becoming marks the difference between the Creator and the creature. Every creature is continually becoming. It is changeable, constantly striving, seeks rest and satisfaction, and finds this rest in God, in him alone, for only he is pure being and no becoming. Hence, in Scripture God is often called the Rock....

The definition given above also affirms God’s unchangeableness or immutability with respect to his purposes. “The counsel of the Lord stands for ever, the thoughts of his heart to all generations” (Ps. 33:11). This general statement about God’s counsel is supported by several specific verses that talk about individual plans or purposes of God that he has had for all eternity (Matt. 13:35; 25:34; Eph. 1:4, 11; 3:9, 11; 2 Tim. 2:19; 1 Peter 1:20; Rev. 13:8). Once God has determined that he will assuredly bring something about, his purpose is unchanging, and it will be achieved. In fact, God claims through Isaiah that no one else is like him in this regard:

I am God, and there is none like me,
declaring the end from the beginning
and from ancient times things not yet done,
saying, “My counsel shall stand,
and I will accomplish all my purpose” . . .
I have spoken, and I will bring it to pass;
I have purposed, and I will do it.
(Isa. 46:9–11)

Furthermore, God is unchanging in his promises. Once he has promised something, he will not be unfaithful to that promise: “God is not a man, that he should lie, or 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 fulfil it?” (Num. 23:19; cf. 1 Sam. 15:29).