"In the beginning was the Word, and the Word was with God, and the Word was God. The same was in the beginning with God. All things were made by him; and without him was not any thing made that was made. In him was life; and the life was the light of men.

... He was in the world, and the world was made by him, and the world knew him not. He came unto his own, and his own received him not. But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth." - John 1:1-4, 10-14 KJV

God revealed the light of His mercy when He made Himself a temple of flesh and blood and dwelt among us. He is the Light. (John 8:12)

"Forasmuch then as the children are partakers of flesh and blood, he also himself likewise took part of the same; that through death he might destroy him that had the power of death, that is, the devil; and deliver them who through fear of death were all their lifetime subject to bondage." - Hebrews 2:14-15 KJV

"…Who hath abolished death, and hath brought life and immortality to light through the gospel:" - 2 Timothy 1:10 KJV

The light of Jesus appeared to Saul of Tarsus (that became Paul the apostle). Paul became a preacher of the gospel to the Gentiles.

"Delivering thee from the people, and from the Gentiles, unto whom now I send thee, to open their eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me." - Acts 26:17-18 KJV

The gospel brought the Gentiles from the darkness of condemnation to the light of God’s mercy by the forgiveness of their sins by repentance, baptism in Jesus name, and the gift of the Holy Ghost. By God’s mercy, found through the gospel, the Gentiles also became God’s chosen people.

"But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar ["(God's own) possession"] people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light: which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy." - 1 Peter 2:9-10 KJV

"For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:" - Ephesians 5:8 KJV

How do we obey the Gospel to become children of light?

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call." - Acts 2:38-39 KJV