By ourselves, it is impossible to escape the demands of justice. And if we are left to ourselves, we will suffer the pains of hell until justice is satisfied. But because God, our Heavenly Father loves us, He has provided a means to satisfy the demands of justice while at the same time snatching us from the torment of hell: His Son Jesus Christ.
There is no other way whereby we can be saved except through the merits and mercy and grace of Jesus Christ. (Mosiah 3:17; Helaman 5:9). And Jesus' nature enabled Him to effectuate His infinite and eternal atonement. Jesus is the Only Begotten of the Father in the flesh, literally the Son of God, possessing all attributes of Godhood. Further, Jesus is also the "seed of the woman," (see Genesis 3:15; Moses 4:21), which gave Him power to subject Himself to death and the afflictions of the flesh. This dual nature made Jesus Christ, and only Him, able to satisfy the demands of justice so He can extend grace to all the inhabitants of the Earth.
Son of God
Jesus Christ is the literal Son of God in the flesh. (Luke 1:31-35; 1 Nephi 11:13-21). Throughout His ministry, Jesus reminded those He taught that Joseph the Carpenter was not His father. (See e.g. Luke 2:42-49 Note Jesus' gentle rebuke when Mary told Him that she and his "father" (Joseph) had "sought [Him] sorrowing: "wist ye not that I must be about my Father's (God's) business). And because God is His Father, Jesus inherited the traits of Godhood and was born free from the effects of the Fall, that is spiritual and physical death.
Remember that spiritual death is to be cut off from the presence of God. (Helaman 14:16-18). There are two spiritual deaths. (Id.). The first happens when we are born. Before Adam and Eve fell, they enjoyed God's presence, and He walked with and talked to them. (See Genesis 3:8; Moses 4: 14-16). But when they fell, God no longer walked and talked with them. (Moses 5:4). And all of us as children of Adam and Eve are under this curse. The resurrection of Christ redeems us from this first spiritual death. (See Redemption from the Fall). The second spiritual death comes because of our sins. When we sin, we cut ourselves off from the presence of God in that we are not worthy to enjoy His presence. This death, as we are currently discussing, can only be overcome through Jesus Christ's atonement.
But Jesus was not subject to either spiritual death. The first spiritual death had no hold on Jesus because His Father was not a descendant of Adam and Eve and, therefore, not subject to the effects of the Fall. Furthermore, although He was tempted in all things, Jesus never yielded to sin. (Hebrews 4:15). Thus, the Father [never] left [Jesus] alone; for [He] [did] always those things that [pleased] [the Father]." (John 8:29). And had Jesus sinned, He would not have been able to suffer for us. Instead, He would have suffered for His own sins.
Think about the times in your life when you felt the closest to God. Imagine feeling that way all day every day. I suppose that is what Jesus felt at all times during His life and ministry. (Yes, there is a significant exception, but to discuss it would put us farther in our discussion than we are prepared to go.)
Physical death had no hold on Jesus either. Through His Father, Jesus received "life in himself." (John 5:26). No one had power to take His life. (John 10:17-18). And if Jesus had wanted, He could have lived forever without tasting death.
Seed of the Woman
While Jesus' Father is God, the Eternal Father, His mother was mortal Mary. Through her, Jesus inherited the traits of mortality. And although His divine nature superseded these traits, Jesus could choose to subject Himself to the infirmities of the flesh, including death. (See Alma 7:10-12). And had Jesus not been born of a mortal woman, He could not have died.
Jesus needed to have this dual nature to satisfy the demands of justice. As the prophet Amulek taught:
And now, behold, I will testify unto you of myself that these things are true. Behold, I say unto you, that I do know that Christ shall come among the children of men, to take upon him the transgressions of his people, and that he shall atone for the sins of the world; for the Lord God hath spoken it.
For it is expedient that an atonement should be made; for according to the great plan of the Eternal God there must be an atonement made, or else all mankind must unavoidably perish; yea, all are hardened; yea, all are fallen and are lost, and must perish except it be through the atonement which it is expedient should be made.
For it is expedient that there should be a great and last sacrifice; yea, not a sacrifice of man, neither of beast, neither of any manner of fowl; for it shall not be a human sacrifice; but it must be an infinite and eternal sacrifice.
Now there is not any man that can sacrifice his own blood which will atone for the sins of another. Now, if a man murdereth, behold will our law, which is just, take the life of his brother? I say unto you, Nay.
The rams and bullocks of the law of Moses could not blot out a person's transgressions. A man being finite and mortal could only suffer for his own sins. Yet the Son of God, even Jesus Christ, being Infinite and Eternal had the capacity to suffer infinitely for all sin. And the Seed of the Woman, had the capacity to suffer death in the flesh, while His divine nature empowered Him to take His body again in the resurrection, never to be separated from it again!