Christ's infinite atonement frees us from the fall of Adam. It allows us to exercise our agency in choosing right and wrong. The term, "free agency" is redundant. It is not found in the scriptures. Rather, the scriptures use the term, "agency of man" (Moses 4:3). People only remain free as long as they exercise this agency wisely. Lehi makes it clear that if they choose the plan of Satan, they are choosing captivity and death. Thus, the wicked voluntarily give up their freedom so that Satan can drag them down to his miserable level.
Joshua tried to help the children of Israel decide how to use their agency righteously, choose you this day whom ye will serve; whether the gods which your fathers served that were on the other side of the flood, or the gods of the Amorites, in whose land ye dwell: but as for me and my house, we will serve the Lord (Josh 24:15). It is only through serving the Lord that we remain free, for we are able to avoid the bondage of sin and the captivity of the devil.
Brigham Young
"You are aware that many think that the Devil has rule and power over both body and spirit. Now, I want to tell you that he does not hold any power over man, only so far as the body overcomes the spirit that is in a man, through yielding to the spirit of evil. The spirit that the Lord puts into a tabernacle of flesh, is under the dictation of the Lord Almighty; but the spirit and body are united in order that the spirit may have a tabernacle, and be exalted; and the spirit is influenced by the body, and the body by the spirit.
"In the first place the spirit is pure, and under the special control and influence of the Lord, but the body is of the earth, and is subject to the power of the Devil, and is under the mighty influence of that fallen nature that is of the earth. If the spirit yields to the body, the Devil then has power to overcome the body and spirit of that man, and he loses both.
"Recollect, brethren and sisters, every one of you, that when evil is suggested to you, when it arises in your hearts, it is through the temporal organization. When you are tempted, buffeted, and step out of the way inadvertently; when you are overtaken in a fault, or commit an overt act unthinkingly; when you are full of evil passion, and wish to yield to it, then stop and let the spirit, which God has put into your tabernacles, take the lead. If you do that, I will promise that you will overcome all evil, and obtain eternal lives. But many, very many, let the spirit yield to the body, and are overcome and destroyed." (Discourses of Brigham Young, p. 69-70 as taken from the Book of Mormon Student Manual, 1981 ed., p. 73-4)