Here is an interesting quote from Evangelical scholar Roger Olson. Feel free to comment.
In the deep background of the clash between Arius and Alexander over the nature of the Logos lay Greek philosophy. It is something both had in common, even if they applied it differently. Both sides of the conflict simply assumed that divinity is ontologically perfect in such a way that any change at all is impossible for it and improper to attribute to it. Thus God, being divine and therefore absolutely perfect, cannot experience change because to change is always to change either for the better or the worse, and in either case God would not be God if he could change.
Absolute static perfection–including apatheia, or impassibility (passionlessness)–is the nature of God according to Greek thought, and nearly all Christian theologians came to agree with this. Of course, they could find in the scriptures several supporting passages that denied change and variability in God. God’s immutability and impassibility, then, became chief attributes of God in Christian theology…
Roger Olson, The Story of Christian Theology: Twenty Centuries of Tradition and Reform“ InterVarsity Press; First Edition edition (April 1999) pg 143