Isaiah's descriptive phrases are sometimes so figurative as to have obscure meanings. Often this is because they have a dual meaning. The implications of verse 20 differ depending on your perspective. The wicked will see the Lord's holy arm of justice at that day in that they will fear him and tremble at his power. The righteous will see his holy arm of mercy at that day in that they will be granted all the promises given to the House of Israel. The scriptures teach us of both perspectives. The holy arm of justice will fall on those who forget God, The Lord who shall suddenly come to his temple; the Lord who shall come down upon the world with a curse to judgment; yea, upon all the nations that forget God, and upon all the ungodly among you. For he shall make bare his holy arm in the eyes of all the nations, and all the ends of the earth shall see the salvation of their God (DC 133:3). Nephi teaches us of his holy arm of mercy, I would, my brethren, that ye should know that all the kindreds of the earth cannot be blessed unless he shall make bare his arm in the eyes of all nations. Wherefore, the Lord God will proceed to make bare his arm in the eyes of all the nations, in bringing about his covenants and his gospel unto those who are of the house of Israel (1 Nephi 22:11).
3 Nephi 17 The Savior blesses the sick, prays for the multitude, and blesses the children
Vaughn J. Featherstone
"Let me tell you the greatest experience I believe I have had in all my readings of the scriptures—and I am sharing something that is very tender with me. I remember the night that I read 3 Nephi the 17th chapter That is when I discovered the Lord Jesus Christ, my Redeemer, the Lord of lords, the King of kings, my Savior, my personal Savior; and I believe that is where I finally found the description of the Savior as I thought him to be. (Elder Featherstone then quoted most of chapter 17)
"…I want you to know I was there. I wouldn't know any more surely if I had been there than I would know having read this book. And I promise you that vicariously every single young man in the Church can read the scriptures and have that same experience with all of the prophets. And you can gain your own testimony, and it need not be pinned on someone else's coat sleeve. You can actually know. You can know that we have a modern prophet. Read his words. Listen to him." (Ensign, Jan. 1973)