To say that God is immutable is to affirm that in His essence, perfections, and purposes, He remains eternally and perfectly the same, never growing, diminishing, or vacillating. While Scripture often speaks of God 'changing' His mind or 'drawing near' to us, Reformed theology understands these as metaphorical expressions—anthropopathisms—that describe His unchanging relationship toward a changing humanity rather than any alteration in His divine nature.
The 1689 LBCF Ch.2 §1 clearly confesses that God is 'immutable,' meaning He is devoid of any potentiality to become something other than what He already is. Because God is pure act, He lacks nothing and can acquire nothing; He is the 'Father of lights, with whom can be no variation, neither shadow that is cast by turning' (James 1:17). As the Lord declares, 'For I, Jehovah, change not' (Malachi 3:6). This doctrine is the bedrock of our hope, for if God could change, He might also change His heart toward His elect or fail to fulfill His promises in Christ.
When Scripture speaks of God 'repenting' or moving toward us, it employs metaphors accommodated to our limited understanding. As noted in Summa Theologica, these are not changes in God's substance but descriptions of how we experience His unchanging goodness. When we draw near to Him, we receive the influx of His grace, appearing to us as a change, even though He remains the same. As it is written, 'God is not a man, that he should lie, neither the son of man, that he should repent' (Numbers 23:19). This protects the integrity of the gospel; because He does not change, the salvation He purchased for us in Christ is eternally secure.