John 9:4 I must work the works of him that sent me, while it is day: the night cometh, when no man can work.
5 As long as I am in the world, I am the light of the world.
It's clear from the context that the reference to the "day" in verse 4 is tied to Christ's statement in verse 5 that as long as He is in the world He is the "light of the world". The implication is that once He leaves the world the light will also leave it and there will be a resulting darkness or night that occurs.
There are some, who read these verses in John 9, in a natural way, and assume that when Jesus speaks of His being in the world it has to do with His physical time on earth.
However, that cannot possibly be the case. Christ declares as long as He is in the world He is the light of the world. If this were to be taken literally, and applied only to His actual time spent on the earth, then it would mean that once He departed the earth to return to heaven the light of the world also departed from off the earth leaving the world in darkness. Since the Bible will not allow for that type of conclusion we must look for another way of understanding Jesus' statement of His being in the world.
The Lord Jesus Christ's declaration that He is the light of the world-has to do with the light of the gospel. And the gospel's light shined long after Christ Himself had left the earth and returned to heaven.
We know that the Bible likens the physical light of the world (the sun) to eternal God (Christ):
Psalm 84:11 For the LORD God is a sun and shield:
Revelation 1:16 ... and his countenance was as the sun shineth in his strength.
The bright burning sun up in the sky typifies the Lord Jesus Christ and His shining forth the gospel into the world.
Alright, so we know that Jesus said He must work the works (salvation) of the One who sent Him (Father) while it was day. By the way, the word "while" should not be overlooked:
Isaiah 55:6 Seek ye the LORD while he may be found, call ye upon him while he is near:
The command to seek God "while" He may be found explicitly implies that a time would come wherein God would be sought and yet not found. For example:
Revelation 9:6 And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them.
The death men seek in the verse above is death that identifies with the death of Christ. Or, to say it another way, seeking death is a figure of speech that points to seeking God's salvation. Yet, they cannot find it. Significantly, the context of Revelation chapter 9 is one of a darkened sun (Revelation 9:2). And again, the sun spiritually represented the fact that Christ is the light of the world. Its darkening indicates that Christ has departed out of the world and no longer is able to perform the work of granting belief (salvation) to sinners.
Jesus performs the work of salvation while it is day. He also declares He is the light of the world. We know that the literal sun (Psalm 84:11) typifies Jesus as the spiritual light of the world.
Jesus also says that the work He's sent to perform (of salvation) cannot be done once it is night. In order for spiritual night to come it must mean that He has gone out of the world.
We also know that the "day" in which Christ says He works ties in with the Day of Salvation and is said to be 12 hours in duration (John 11:9,10). The parable of hiring workers to go work in the vineyard points to a 12 hour work day. The 12 hours of work in the vineyard relates to the work Christ does in His people as they bring the gospel to the world during the prolonged period of the "Day of Salvation". In the parable, the work day (of salvation) comes to an end after an unusual hiring of workers at the 11th hour who work only one hour until the day ends at the 12th hour. This last hour of work (salvation) ties in with the Great Tribulation period which is likened to one hour in a few Scriptures. Of course, historically, the reason why workers stopped working after 12 hours was due to the sun going down and the night following.
We have known for some time now that the Great Tribulation period (the one hour which identifies with the 11th to the 12th hour of the parable of the workers going to work in the vineyard) has already finished. The Great Tribulation period finished on the date of May 21, 2011.
What does the Bible tell us happens after the tribulation finishes? See:
Matthew 24:29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
The first thing God wants us to know about the end of the tribulation is-the sun is darkened.
Why does God want us to know this? The answer is because Jesus is the light of the world. And while it was light throughout the prolonged Day of Salvation He performed the work of saving sinners. But that work day (of salvation) in God's vineyard concluded once the Great Tribulation (one hour- 11th hour to 12th hour) completed. The spiritual night has followed the day and within this night no man (Christ) can do the work of salvation.