First, the Greek verbs in John 1:4 - there are two here and both the same: ἦν (en) = "was"; which is imperfect, indicative, active, 3rd person singular. The fact that it is an imperfect verb means that that John intends to convey that Jesus was the light and remains the light - the imperfect verb means the action does not stop.
John's theme of Jesus being characterized by "light" is frequent in his writings. He uses the idea in two separate ways:
- John 17:5 - And now, Father, glorify Me in Your presence with the glory I had with You before the world existed.
- 1 John 1:5 - And this is the message we have heard from Him and announce to you: God is light, and in Him there is no darkness at all. Compare Gen 1:3, Eze 1:27-28
- Dan 10:6 - His body was like beryl, his face like the brilliance of lightning, his eyes like flaming torches, his arms and legs like the gleam of polished bronze, and his voice like the sound of a multitude.
- Rev 1:14-16 - The hair of His head was white like wool, as white as snow, and His eyes were like a blazing fire. His feet were like polished bronze refined in a furnace, and His voice was like the roar of many waters. ... His face was like the sun shining at its brightest.
- 1 Thess 2:8 - And then the lawless one will be revealed, whom the Lord will consume with the breath of His mouth and destroy with the brightness of His coming.
- 1 Tim 6:16 - He alone is immortal and dwells in unapproachable light.
John also uses this same idea metaphorically to teach about spiritual illumination.
- 1 John 1:6, 7 - If we say we have fellowship with Him yet walk in the darkness, we lie and do not practice the truth. But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus His Son cleanses us from all sin.
- John 8:12 - Once again, Jesus spoke to the people and said, “I am the light of the world. Whoever follows Me will never walk in the darkness, but will have the light of life.”
- John 9:5 - While I am in the world, I am the light of the world.
- John 12:46 - I have come into the world as a light, so that no one who believes in Me should remain in darkness.
- Matt 4:16 - the people living in darkness have seen a great light; on those living in the land of the shadow of death, a light has dawned.
- Luke 2:32 - a light for revelation to the Gentiles, and for glory to Your people Israel.
- Eph 5:13 - But everything exposed by the light becomes visible, for everything that is illuminated becomes a light itself.
- Col 1:12 - giving thanks to the Father, who has qualified you to share in the inheritance of the saints in the light.
- 1 Peter 2:9 - But you are a chosen race, a royal priesthood, a holy nation, a people for his own possession, that you may proclaim the excellencies of him who called you out of darkness into his marvelous light.
... and so forth. The best discussion of this metaphor of light is found in John 9 when Jesus healed the man born blind and then used this as a teaching device that the blind could not see the light of Christ's teaching.
39 Then Jesus declared, “For judgment I have come into this world, so that the blind may see and those who see may become blind.” 40
Some of the Pharisees who were with Him heard this, and they asked
Him, “Are we blind too?” 41 “If you were blind,” Jesus replied,
“you would not be guilty of sin. But since you claim you can see, your
guilt remains.” John 9:39-41
John 1:4 - In Him was life, and that life was the light of men.
This is a very succinct statement that Jesus is the source of life AND that fact is what illuminates the mind of believers and inspires their hope in the future provided by Jesus.
Benson comments as follows:
He, who is essential life, and the author of life to all that live,
was also the fountain of wisdom, holiness, and happiness to man in his
Barnes is more expansive:
The life was the light of men - "Light" is that by which we see
objects distinctly. The light of the sun enables us to discern the
form, the distance, the magnitude, and the relation of objects, and
prevents the perplexities and dangers which result from a state of
darkness. Light is in all languages, therefore, put for "knowledge" -
for whatever enables us to discern our duty, and that saves us from
the evils of ignorance and error. "Whatsoever doth make manifest is
light," Ephesians 5:13. See Isaiah 8:20; Isaiah 9:2. The Messiah was
predicted as the "light" of the world, Isaiah 9:2, compared with
Matthew 4:15-16; Isaiah 60:1. See John 8:12; "I am the light of the
world;" John 12:35-36, John 12:46; "I am come a light into the world."
The meaning is, that the λόγος Logos or Word of God is the
"instructor or teacher" of mankind. This was done before his advent by
his direct agency in giving man reason or understanding, and in giving
his law, for the "law was ordained by angels 'in the hand of a
mediator'" Galatians 3:19; after his advent by his personal ministry
when on earth, by his Spirit John 14:16, John 14:26, and by his
ministers since, Ephesians 4:11; 1 Corinthians 12:28.