The principle of Agency has been around for thousands of years, and is taken for granted. For example, real estate agents represent sellers to potential buyers; they speak for them.
The first reference to Agency in the Bible is in Genesis 24, where Abraham’s chief steward represents him in finding and choosing a bride for Isaac. An agent acts on behalf of another person. The agent is regarded as identical to the one he represents.
So, in Exodus 4:15-16 we read that Aaron is to speak to Pharaoh as Moses, and Moses “as” God. As agents of God, angels have no voice of their own but simply speak as directed by the LORD (Genesis 18). Jacob “wrestled with God in the form of “the Angel of the LORD (Genesis 32:24-30 & Hosea 12:3-4). Genesis 48:15-16 refers to the Angel of the LORD as the LORD Himself.
In Judges 13:18, the Angel of the LORD says that his name is Secret. In verse 20, Manoah sees the Angel of the LORD and is fearful because he has “seen God”! In Exodus 23:20, God says of the Angel of His presence: “My Name is in Him.” The Angel has His reputation, His honour, His character. The judges of Israel are referred to in Psalm 82:6 as “gods” because they represented Him to the people; they applied His Word. Jesus quoted this verse to the Jewish leaders when they accused him of making himself God (John 10:33-36).
Agency explains why God as Principal is “the First and the Last” and Jesus as Agent is called the same. In Revelation 22 the Angel rejects John’s worship and refers to himself as a servant, just like John, and yet in the next verse speaks as Jesus in the First Person! Jesus came in his Father’s Name, and as such was given “authority on earth to forgive sins” and to impart life at will (John 5:23) As God’s Supreme and Final Agent, Jesus, the Son of God, is spoken of in the same terms as his Father (John 15:23).
This principle of Agency explains so many texts in John that otherwise would be inexplicable. In Philippians 2:6, Paul writes: “Let each of you look out not only for his own interests, but also for the interests of others.”
In other words, they should represent one another, not just themselves. Paul continues: “Let this mind be in you which was also in Christ Jesus, who being in the form of God (“morphee” — “in another form, one that perfectly represented God”, #3444 Strong’s) — thought it not robbery to be equal with God (thought it not a thing to be grasped and selfishly held to oneself as a prize) but made himself of no reputation (the Agent/Son of God not selfishly holding on to his status as such, but taking on himself the form of a humble servant. Which is what an angel does when speaking to John, and then for God, in Revelation 22:7-13.