Jehovah`s Witness/a testing of spirits
American Standard Version (ASV)
9 In all their affliction he was afflicted, and the angel of his presence saved them: in his love and in his pity he redeemed them; and he bare them, and carried them all the days of old.
10 But they rebelled, and grieved his holy Spirit: therefore he was turned to be their enemy, and himself fought against them.
11 Then he remembered the days of old, Moses and his people, saying, Where is he that brought them up out of the sea with the shepherds of his flock? where is he that put his holy Spirit in the midst of them?
12 that caused his glorious arm to go at the right hand of Moses? that divided the waters before them, to make himself an everlasting name?
13 that led them through the depths, as a horse in the wilderness, so that they stumbled not?
Who is the angel in verse 9, and who or what is the arm in verse 12?
The short answer to your question is Jesus Christ!
The Scriptures indicate to us that IT was Jesus who guided the Israelites during their deliverance from Egypt and been with them throughout the years of their sojourn.
As the Scripture tells us:
“Then the angel of the [true] God who was going ahead of the camp of Israel departed and went to their rear, and the pillar of cloud departed from their van and stood in the rear of them. 20 So it came in between the camp of the Egyptians and the camp of Israel. On the one hand it proved to be a cloud together with darkness. On the other hand it kept lighting up the night. And this group did not come near that group all night long.” (Exodus 14:19, 20)
Notice the same angel of the true Go is also mentioned in the following verses..
““Here I am sending an angel ahead of you to keep you on the road and to bring you into the place that I have prepared. 21 Watch yourself because of him and obey his voice. Do not behave rebelliously against him, for he will not pardon YOUR transgression; because my name is within him.” (Exodus 23:20, 21)
“And now, come, lead the people to where I have spoken to you of. Look! My angel will go ahead of you, and on the day of my bringing punishment I shall certainly bring punishment upon them for their sin.”” (Exodus 32:34)
“And I will send an angel ahead of you and drive out the Ca′naan·ites, the Am′or·ites, and the Hit′tites and the Per′iz·zites, the Hi′vites and the Jeb′u·sites;” (Exodus 33:2)
“Finally we cried out to Jehovah and he heard our voice and sent an angel and brought us out of Egypt; and here we are in Ka′desh, a city at the extremity of your territory.” (Numbers 20:16)
“This Moses, whom they disowned, saying, ‘Who appointed you ruler and judge?’ this man God sent off as both ruler and deliverer by the hand of the angel that appeared to him in the thornbush.” (Acts 7:35)
These scriptures gives a clue as to the identity of this angel sent by God.
Exodus 23:21 says: "my name is within him.”
There's no other angel mentioned in the Bible where God personally said:
"Watch yourself because of him and obey his voice"
"Do not behave rebelliously against him, for he will not pardon YOUR transgression;
"because my name is within him.”
There's Michael the Arc-angel (Micha.el means Who Is Like God?")
Then there's Jesus whose name means "Salvation of Jah"
Both name indicates that Jehovah's name is attached to their names.
So is it Michael or Jesus?
Actually both because both names refer to the same person. The Person who we came to know as Jesus Christ.
Here's additional proof that it was Jesus:
“Now I do not want YOU to be ignorant, brothers, that our forefathers were all under the cloud and all passed through the sea 2 and all got baptized into Moses by means of the cloud and of the sea; 3 and all ate the same spiritual food 4 and all drank the same spiritual drink. For they used to drink from the spiritual rock-mass that followed them, and that rock-mass meant the Christ.
” (1 Corinthians 10:1-4)
As for the "arm" in v12 of Isa 63: It's an expression of Jehovah God's mighty saving power!
“‘O Sovereign Lord Jehovah, you yourself have started to make your servant see your greatness and your strong arm, for who is a god in the heavens or on the earth that does deeds like yours and mighty performances like yours?” (Deuteronomy 3:24)
“For it was not by their own sword that they took possession of the land, And their own arm was not what brought them salvation. For it was your right hand and your arm and the light of your face, Because you took pleasure in them.” (Psalm 44:3)
“O Jehovah, show us favor. In you we have hoped. Become our arm every morning, yes, our salvation in the time of distress.” (Isaiah 33:2)
There's more scriptures but I think the ones quoted above are more than enough. If not please follow up.
Hope this helps.