6a For to us a child is born, to us a son is given; ~ Isaiah 9:6a
When Isaiah prophesied that a child would be born, but a son is given, he was actually describing the Messiah. When he said a child is born, he was speaking about Jesus’ natural birth. He was describing His human nature that He inherited through His earthly mother, Mary.
Jesus could not come as God and die as God to save mankind. Jesus had to set off His Godliness so that He could come as a man and die as a man. Why? Because He was taking the place of mankind. Jesus took our sin upon Himself and died so that we didn’t have to. So that anyone who calls on the name of the LORD will be saved.
Unto us a son is given, speaks about His divinity. Jesus was the second member of the Godhead before His incarnation and remained the second member of the Godhead after His death and resurrection. When Paul wrote, “did not count equality with God a thing to be grasped,” he was saying that Jesus did not count, think, or consider being equal to God, something that was obtainable by mere human beings. We do not and cannot obtain Godhood.
Then the Word emptied Himself is the Greek word kenosis meaning to empty. So, what Paul was explaining is that Jesus, although He was God and is still God, did not take advantage of being God, but rather, He emptied Himself of it, or in other words, put it to one side so that He could operate as a mere man, but still retain His Godhood. And that is the reason the prophet said, unto us a child is born, and unto us a son is given. Because Jesus Christ, our LORD and Savior, is both God and man.
Peace. Love. Go Forth and Accept His Free Gift of Salvation.