Hello Shauna,
You are correct that the term "free agency" is uniquely RLDS. The term roughly correlates with the concept of "free will" in Christian theology. In your note you explore the concept of free will and wonder how that fits together with the concept of the sovereignty of God. People have struggled with the tension between these two concepts for millennia. These two extremes are represented in the theologies of John Calvin and Jacobus Arminius. Calvin built his theology around the sovereignty of God, while Arminius built his around the free will of mankind. The five primary points of Calvin's theology spell the acronym TULIP, which stand for 1) the Total depravity of mankind, 2) the Unconditional election of God, 3) the Limited atonement of Christ, 4) the Irresistible grace of God and 5) the Perseverance of the Saints. It is Calvin's doctrine of Unconditional election which portrays the sovereignty of God; He alone decides our destiny for us, we have no voice or say in the matter. On the other end of the spectrum is the concept of mankind's free will, which is championed in the theology of Arminius. Many Baptist denominations follow Calvin's theology, while certain Methodists, the Assemblies of God and other Pentecostal denominations follow Arminian theology.
I mentioned above, people have exhausted themselves over the centuries trying to reconcile the tension between these two extremes. This includes many Christian theologians. The theologies of Calvin and Arminius are useful in this regard primarily because they define the extreme positions, and thereby they help define the issues and the debate. But in reality, the truth likely falls somewhere in the middle, not at either extreme. As humans, we have trouble with things which leave us in tension. But when we consider a number of the attributes of God, we are left with no choice. For example, in this present sphere of existence, humans cannot adequately grasp the concept of eternity, in respect to either time or space. We may try to appreciate it, but in actuality we simply cannot apprehend it fully. The same is true of the Trinity, how the Father, the Son and the Holy Spirit can all be separate in some sense, yet a complete unity in another sense. We try to display our understanding of this mystery by developing analogies which seem to make sense to us. But the truth remains that the concept is simply beyond our present level of understanding. That's what makes God the supreme creator, and what makes us humans, the created ones. " 'For my thoughts are not your thoughts, neither are your ways my ways,' declares the LORD. 'As the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts' (Isaiah 55:8-9)." The fact is, we simply are not smart enough to figure out God, and His ways. We can try, and I think we should; God wants us to seek after Him. But we should also admit when He is far too big for us. Isn't it presumptuous to feel that we are bright enough to master the deep things of God, to "put Him in a box" if you will? In doing so, I feel we try to place ourselves at His level, which we simply are not.
As with the concepts of eternity and the Trinity, humans struggle with the tension between Predestination and Free Will. And yet we have to confess that harmony between the two escapes us in our present condition. Consider the following two statements of Jesus. "Whosoever will come after me, let him deny himself, and take up his cross, and follow me (Mark 8:34, KJV)." and "No man can come to me, except the Father which hath sent me draw him (John 6:44, KJV)." If we take either of these statements in isolation--and many other similar statements in scripture--we run the risk of ending up at one of the extremes. However, when we consider these statements together, we end up in tension. And I believe that until we see Him face to face we will just have to live with that tension, as uncomfortable as it may feel at the present time.
As you point out, Joseph Smith added to this tension by coming up with the erroneous concept of an American Zion, and then holding his church responsible for its fulfillment. As you say, God's "hands would be tied" until Latter Day Saints became good enough to bring about this God ordained condition. Joseph Smith's statements in this regard have made countless people across many generations feel guilty for not being "good enough" to bring about "Zion." "Were it not for the transgressions of my people...they might have been redeemed even now (D&C 102:2a)." This is so very unfortunate, and so very erroneous. It has been an extremely liberating experience for people to be released from this erroneous teaching once they realize that Joseph Smith was a false prophet, myself included. I explain Joseph Smith's unbiblical concept of an American Zion in chapter 3 of my book Part Way to Utah: the Forgotten Mormons.
As you say, God will clearly bring His will to pass, with or without our cooperation. But at the same time He entices us to use our free will to join Him in His work on earth, and become the heirs of His wonderful salvation, a home in His eternal Kingdom. Until we see Him face to face in His Kingdom, however, we will likely not understand how both of these statements compliment each other; but will likely continue to see them in tension.
Hope this has been helpful Shauna.
God's blessings to you,
Paul Trask