Principle: Because it was certain that Jesus Christ would complete the Atonement, its effects were already in place in the premortal world.
Read 1 Nephi 7:1-7:15
In verse 5 Nephi relates how "the Lord did soften the heart of Ishmael." Return again and read 1 Nephi 1:20; how did faith lead to deliverance for Ishmael? The effects of the Atonement of Jesus Christ impacted the families of Lehi and Ishmael even before Christ came to the earth. From what you have read how could this be possible?
Before coming to earth all the children of Heavenly Father were with Him. At this time Satan rebelled and drew others to his teachings. Read Revelation 12:7-11 and look for characteristics of this war.
Elder Bruce R. McConkie taught "What kind of war [was the War in Heaven]? The same kind that prevails on earth; the only kind Satan and spirit beings can wage - a war of words, a tumult of opinions, a conflict of ideologies; a war between truth and error" (Doctrinal New Testament Commentary, 3 vols. [1965-73], 3:518).
How is the War in Heaven similar to the war Satan wages against God's children in mortality?
Cross reference Revelation 12:10 and Moses 4:3
How was the "accuser of our brethren" (Satan) cast from the premortal world?
Review the principle of the day and Revelation 13:8, Mosiah 4:7, and Moses 7:47
The power of Christ was available in the premortal world, how can you access that same power to overcome the war Satan rages today?