Mosiah 15:1 - 15:5

Mosiah 15:1 And now Abinadi said unto them: I would that ye should understand that God himself shall come down among the children of men, and shall redeem his people.

The bottom line is that God, Himself, will come down and become a mortal and personally redeem us all.
[This is unlike the traditions of the world, where it is taught that we have to sacrifice humans to appease the Gods. In our doctrine, it is God that is sacrificing Himself to appease us.]

Mosiah 15:2 And because he dwelleth in flesh he shall be called the Son of God, and having subjected the flesh to the will of the Father, being the Father and the Son—

Because He will become a mortal, he will be referred to as a “son.” And since He will live a sinless life, He will be referred to as the Father. So He is both Father and Son.
[It appears that the title of Father and Son have more to do with accomplishments toward perfection as apposed to relationship by birth.]

Mosiah 15:3 The Father, because he was conceived by the power of God; and the Son, because of the flesh; thus becoming the Father and Son—

So Christ is both Father and Son because He was the actual son of God and that He was subject to death as a mortal.

Mosiah 15:4 And they are one God, yea, the very Eternal Father of heaven and of earth.

So taking these two accomplishments together, Christ is both Father and Son or one person with both attributes.

Mosiah 15:5 And thus the flesh becoming subject to the Spirit, or the Son to the Father, being one God, suffereth temptation, and yieldeth not to the temptation, but suffereth himself to be mocked, and scourged, and cast out, and disowned by his people.

His accomplishment then was to control His mortal desires by the power of His spirit and live up to the commands of His Father. He was thus able to ignore temptation, and allow Himself to be made fun of, beaten, run out of towns and rejected by His people, the Jews.
[Considering that He had the power to destroy anyone with a command, it is a remarkable restraint of power on His part. He never let His temper get the best of Him. He had so much love for His people that He would allow them to treat Him as such, knowing what He was accomplishing would be of great value to them even though they could not see it at the time.]