The Arm of the Lord is an Old Testament title for Jesus in the Old Testament. The reason we recognize this is because the Arm of the Lord is distinguished from the Father the same way Jesus is, does the things only God can do, and is directly identified by the New Testament authors as who the prophets were referring to when this title came up.
1. The Arm of the Lord is distinguished from the Father the same way Jesus is.
2. The Arm of the Lord is equal to the Father the same way Jesus is.
3. The Arm of the Lord is described doing all of the things Jesus is credited for.