Bear in mind these are somewhat terms of art in the theology. It flows from the attributes of God as immutable, unchanging, etc.
For explanation of the Orthodox view, here's some excerpts from "An Exact Exposition of the Orthodox Faith" by St John Damascene:
Concerning the Holy Trinity.Therefore, theologically, disagreement over passion in this sense would involve disagreement with the other attributes as well or the logic of the theology it derives from.
We believe, then, in One God, one beginning, having no beginning, uncreate, unbegotten, imperishable and immortal, everlasting, infinite, uncircumscribed, boundless, of infinite power, simple, uncompound, incorporeal, without flux, passionless, unchangeable, unalterable, unseen, the fountain of goodness and justice, the light of the mindHow could that be immutable which is circumscribed and subject to passion? And how could that be passionless which is composed of elements and is resolved again into them? For combination is the beginning of conflict, and conflict of separation, and separation of dissolution, and dissolution is altogether foreign to God
Wherefore in God, Who alone is passionless and unalterable, and immutable, and ever so continueth, both begetting and creating are passionless. For being by nature passionless and not liable to flux, since He is simple and uncompound, He is not subject to passion or flux either in begetting or in creating, nor has He need of any co-operation
He is passionless and incorporeal: independent of the union of two again because He is incorporeal but also because He is the one and only God, and stands in need of no co-operation: and without end or cessation because He is without beginning, or time, or end, and ever continues the same.
thanks for your reply.
Actually, the failure comes in not understanding the nature of passions.
God is not subject to passions, because God is always in control of passions.
God's passions are always controlled by His other attributes, so they respond accordingly.
A passionless God would be a loveless God, which is the opposite of what the Scripture states God is.
Passion is a problem in man because he allows sinful thoughts to control them.
But when the Holy Spirit controls the man, then the passions that are produced are Divine Like, Love, Joy, Peace, Longsuffering, gentleness goodness, meekness, faith, temperance.
Immutability does not move that God is either immovable or unfeeling, only that He never contradicts or violates any of His perfect attributes.
Thus, God's feelings are always perfect as well.
A God without passion (feeling) is not the God of the Bible.