"I assure you: An hour is coming, and is now here, when the dead will hear the voice of the Son of God, and those who hear will live.John 5:25(HCSB)
The eternal Son of God has had life in Himself from before time began, before space was created, before matter was spoken into being, and before man was formed from the dust of the ground. But because of Adam's sin, every man is born into this physical world spiritually dead - dead in trespasses and sins, at enmity with God, facing eternal separation from his Creator, and without hope in the world.
However, for four thousand years God had been preparing a Body for His eternal Son, Whom He had purposed would become the Kinsman-Redeemer of Adam's fallen race. He would be the Seed of the woman Who would be secretly passed down the generations, in order to be born into His own creation as the perfect Son of Man.
The eternal Son of God Who had life in Himself from eternity past, was born into the human race that He Himself had created in His own image and likeness. He was the perfect Son of Man Who would willingly give His own life as the only acceptable ransom-price for the sin of the whole world.
It would be through the sacrificial death of His own life, and for the sake of fallen man, that the perfect Son of Man would receive authority from on high to give His resurrected life to all who would believe on His name. And so we read in this verse that the time had finally arrived for the dead to hear His voice and be raised up again, and Christ announced, "Assuredly I say to you that an hour is coming, and is now here, when the dead will hear the voice of the Son of God, and those who hear will live."
The Lord Jesus was not simply referring to the physical resurrection of people like Lazarus, Jairus' daughter, or the dead son of the widow of Nain, but to all who would hear and receive His message of salvation, and trust in His own redeeming blood for the forgiveness of sin and life everlasting.
God alone can forgive sins and He alone can give life, but God is Spirit and only the shed blood of a perfect Man could atone for the sins of the whole world. Only God in the flesh could pick up His cross, learn obedience by the things that He suffered, walk the way of the death and raise Himself from the dead so that His resurrected life could be imparted to all who believe in Him.
And so in His grace, the eternal Son of God stripped Himself of His heavenly garments and was made in the likeness of sinful man so that by His sacrificial death and glorious Resurrection, He would rise to life immortal and be given the authority from on high to give His resurrected life to all who would trust in His sacrificial death for salvation.
Heavenly Father, I do not know or understand a fraction of the cost for the eternal Son of God to come in the likeness of sinful flesh and willingly sacrifice His life for me, as the suffering Son of Man. But I praise and thank You that by His sacrificial death and glorious Resurrection, many who were dead in sins have heard His voice and been given a new-life-in-Christ for the forgiveness of sins and life everlasting. Praise His holy name, AMEN.