Another criticism against postmillennialism is based on passages that suggest few will be saved, such as
13"Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it. 14"For the gate is small and the way is narrow that leads to life, and there are few who find it. (Matt. 7:13-14)
We could stop here, but this is interesting enough (I suspect) that we should see how postmillennialism answers this.
This and similar passages (Matt 22:14) must stand side-by-side with passages that indicate vast multitudes in heaven:
After this I looked and there before me was a great multitude that no one could count, from every nation, tribe, people and language, standing before the throne and in front of the Lamb. They were wearing white robes and were holding palm branches in their hands. (Rev 7:9)
And, shortly after he uttered the words of Matt. 7:13-14 above, Jesus said:
I say to you that many will come from the east and the west, and will take their places at the feast with Abraham, Isaac and Jacob in the kingdom of heaven. (Matt. 8:11)
The word polus for "many" (who will be saved) in Matt. 8:11 is the same word translated to "many" (on the path of destruction) in Matt 7:13. Elsewhere Jesus promises that His father’s house has many rooms (John 14:2).
How can this be? First of all, that the path is narrow is not relevant. A mountain pass can be narrow and treacherous, yet a competent guide can lead the majority of his charges safely through. Nobody denies the path is narrow: Jesus is the only way to eternal life. Still there is the aspect that few will find the narrow gate.
There are two possibilities of reconciliation. One is that the verses don't mean what a plain reading would indicate. That seems unlikely. The verses quoted here and others relevant for this debate are straightforward. The better explanation is, propose by Warfield and others: some of these verses are prophetic, some are contemporary and ethical. Postmillennialists believe that verses such as Rev. 7:9 and Matt. 8:11 are prophecy. Matt. 7:13-14, on the other hand, is a call to the apostles to get to work—do not sit back and rest on God's Sovereignty. So few in those early days chose to follow Christ, but that does not imply that such will be the case in all ages. Matt. 7:13-14, in this perspective, is the initial ethical motivation of the Great Commission, similar to Paul's call to witness in Rom. 10:14-15.
Even "ambiguous" passages, such as the Dragnet parable:
47 "Again, the kingdom of heaven is like a dragnet cast into the sea, and gathering fish of every kind; 478 and when it was filled, they drew it up on the beach; and they sat down and gathered the good fish into containers, but the bad they threw away. (Matt. 13:47-48)
and the famous book of life passage
If anyone's name was not found written in the book of life, he was thrown into the lake of fire. (Rev 20:15)
Have, according to postmillennialists, a tone that suggests while evil is present until the end, it is the exception to the rule. The dragnet (kingdom of heaven) pulls in many fish, the catch is mostly good, but some are thrown out. It seems to be presented as the exception that a name is not in the book of life. And in the parable of the wheat and tares (Matt. 13:14-29; 36:43), we find the angels harvesting a wheat field that contains some weeds, not a weed field with a smattering of wheat.