Scripture uses many metaphors to explain a concept, and the word "arm" promotes a vivid image of God's strength and power. The arm (from the shoulder down to the fingertips) is an EXTENSION of the body - a vital part of the body, DOING things such as lifting, grasping, punching, holding ... its every action controlled by the brain. We humans "lift up our arms" to praise ADONAI...
The arm only moves according to the signals sent from the brain. Without the brain, the arm could do nothing. In Isaiah 59:16 and 63:5, the prophet tells how YHWH will save his people by his "own arm"; and in Isaiah 53:1 we see this amazing prophetic picture of Y'shua:
"Who believes our report? To whom is the arm of Adonai revealed?" and then it goes on to describe a human man - a description that perfectly fits Y'shua in every way!
Y'shua is "the ARM of YHWH" because YHWH caused His Divine Messiah (His"arm") to be born as a human being (someone humanity could identify with and understand), and grow up to preach the Kingdom, do everything His FATHER commanded, and then to offer/sacrifice himself on our behalf, thus eliminating the need for animal SIN sacrifices.
(NOTE: Y'shua did NOT abolish the need for any other sacrifices, such as the ones we see in Leviticus 7:37 - burnt, grain, sin, guilt, consecration and peace ofeerings. We cannot do them today because there is no Temple, but they will be reinstituted again, once the Third Temple is built.)
It is imperative to understand that the "arm" doesn't control the "brain"; said another way: Yeshua never suggested that he came to replace YHWH/the "Father" in any way! He came to do everything the Father TOLD him to do...
Luke 4:43 "But he (Yeshua/Jesus) said, "I must preach the good news of the Kingdom of God to the other towns also, because that is why I was sent."
Luke 8:1 And it happened after these things that Y'shua was going around in the cities and in the villages and was preaching and declaring the Kingdom of Elohim.
As you know, Messiah Y'shua was different from any other human because he was the "Arm" of YHWH (Isaiah 53:1, AND the "Word" John 1:1 and 14). As such, he was a "divine" and indelible part of YHWH, which maked him ONE with YHWH. (A "part" of the body belongs to the WHOLE body, and is a vital part of that body.)
BOTTOM LINE: In the case of Y'shua, the Ruach (Spirit of YHWH) was encased in the flesh of the SON, and it is that flesh which was pierced. YHWH Himself was never pierced; YHWH Himself was neither born nor died - for, had that been the case, He would have been no different from humans ... and a mere human CANNOT be ELOHIM.
But His "arm" - His ARM /POWER/ STRENTH - represented by the human being named Y'shua (which is Hebrew for "YHWH is Salvation"), the ONLY Heavenly being who has the actual NAME of יהוה (the Hebrew letters "Yud-Hey-Vav-Hey") within his own name, reached out to humanity to show how to be "set apart" from a lost world where sin and death rule, so that we may be found "clean" in body, soul and spirit and thus receive the gift of Eternal Life (Genesis 2:7; 1 Thessalonians 5:23; Matthew 10:28; Ecclesiastes 12:7; 1 Corinthians 6:19-20; 1 John 5:20, etc.).
John 17:1. Y’shua spoke these things and he lifted up his eyes to Heaven and said My Father the hour has come. Glorify your Son so that your Son might glorify you. 2. Just as you have given him authority over all flesh that whomever You have given him, he will give to him life that is eternal.
3. Now this is life that is eternal, that they might know You, that You are the Elohim of Truth, and he alone whom You have sent, the Mashiyach Y’shua. 4. I have glorified You on earth. The work that You have given to me to do I have finished it. 5. And now glorify me my Father with You in that glory that I had with You from before the world was. 6. I have made Your Name known to the sons of those men whom You had given to me from the world. (AENT)