"Did Christ have free will?"
Christ is God, the origin and definition of Free Will.
Before the Fall, Adam was in a state of potential theosis, though likely far more advanced than any of us. His free will was natural to him and not at all a flaw. Free Will is an attribute of our Triune God and Adam was created in the image and likeness of God. The exercise of that Free Will, to gain knowledge when he wasn't ready for it and then lying about it to God was Adam's doing, Adam's sin, not God's. God is never the author of evil, my friend.
Man's natural state is the state of Adam before the Fall and it is the state, theosis, to which we aspire and through the Incarnation it is available to us as it was to Adam. +Gregory Palamas gives a good discussion of this:
"Adam, before the fall ... participated in ... divine illumination and resplendence [theosis, or potential theosis], and because he was truly clothed in a garment of glory he was not naked, nor was he unseemly by reason of his nakedness. He was far more richly adorned than those who now deck themselves out with diadems of gold and brightly sparkling jewels. St. Paul calls this divine illumination and grace our celestial dwelling when he says, 'For this we sigh, yearning to be clothed in our heavenly habitation, since clothed we will not be found naked' (2 Cor. 5:2)."
"But, what I didn't catch was why this apparently was such a big deal. It appeared to be a major reason for the schism, but I don't see why that would be."
It is just about the most major big deal in Christian theology after the Arian and Nestorian heresies. The issue of the Procession of the Holy Spirit has to do with the monarchy of the Father and the inner relationships of Holy Trinity and implicates questions of created and uncreated energies of God. Originally the filioque was used in Spain to counter certain Christologic heresies of the Arians. For centuries it was condemned by all the Patriarchs, including Rome, but eventually Rome accepted it and inserted it in the Creed. The East never accepted that. It now appears that Rome agrees that the use of the filioque is not "normative" and that it shouldn;t be used for teaching and translations. Some today say that although the filioque as originally taught by Rome is problematic, nevertheless it really is more about words than belief. The Church of Rome and the Orthodox Churches of the East agree that while the Holy Spirit is sent by both the Father and the Son, the Holy Spirit "proceeds" only from the Father which is the source of both the Son and the Spirit. In any event, +Gregory Palamas explains the workings of the Trinity about as well as anyone could (for the Latins who read this, note how +Gregory speaks of the "eros" between the Father and the Logos and compare to +Benedict XVI's recent, quite wonderful, encyclical):
"The Spirit of the supreme Logos is a kind of ineffable yet intense longing or 'eros' experienced by the Begetter for the Logos born ineffably from Him, a longing experienced also by the beloved Logos and Son of the Father for His Begetter; but the Logos possesses this love by virtue of the fact that it comes from the Father in the very act through which He comes from the Father, and it resides co-naturally in Him.
It is from the Logos's discourse with us through His incarnation that we have learned what is the name of the Spirit's distinct mode of coming to be from the Father and that the Spirit belongs not only to the Father but also to the Logos. For He says 'the Spirit of Truth, who proceeds from the Father' (John 15:26), so that we may know that from the Father comes not solely the Logos - who is begotten from the Father - but also the Spirit who proceeds from the Father. Yet the Spirit belongs also to the Son, who receives Him from the Father as the Spirit of Truth, Wisdom and Logos. For Truth and Wisdom constitute a Logos that befits His Begetter, a Logos that rejoices with the Father as the Father rejoices in Him.
This accords with the words that He spoke through Solomon:'I was She who rejoiced together with Him' (Prov. 8:30). Solomon did not say simply 'rejoiced' but 'rejoiced together with'. This pre-eternal rejoicing of the Father and the Son is the Holy Spirit who, as I said, is common to both, which explains why He is sent from both to those who are worthy. Yet the Spirit has His existence from the Father alone, and hence He proceeds as regards His existence only from the Father. Our intellect, because created in God's image, possesses likewise the image of this sublime Eros or intense longing - an image expressed in the love experienced by the intellect for the spiritual knowledge that originates from it and continually abides in it."
Wow.
So "sending" is not the same as "procession as regards existence"? My Catholic lung feels fine. Does this satisfy my Orthodox lung?
Christ is God, the origin and definition of Free Will. Before the Fall, Adam was in a state of potential theosis, though likely far more advanced than any of us. His free will was natural to him and not at all a flaw. Free Will is an attribute of our Triune God and Adam was created in the image and likeness of God. The exercise of that Free Will, to gain knowledge when he wasn't ready for it and then lying about it to God was Adam's doing, Adam's sin, not God's. God is never the author of evil, my friend.
Firstly, I fully agree that God is not the author of evil, I have said so explicitly several times on this thread. My premise for asking the question was that Adam was not created in perfection, because he had the free will to sin, and of course, he did. In heaven, there is no sin, so we will be "perfect" then, although not equal to God or His essence in any sense. So, another way to ask my same question would be: "could Jesus have used His free will and sinned"? I would answer 'No', not because He doesn't have the power to do whatever He wants, but because it is not His nature to sin. The incarnation of Jesus was in perfection, unlike Adam.
Thank you very much for your comments on the filioque. That was very informative.