What then, does ‘outer darkness’ refer to? It's very simple. When we read these things, we read it through western culture, rather than looking at the original culture. In the original culture, the context of the last parable was what? It was the virgins, that went into the marriage feast, the Marriage Supper. What would that look like?
Well, in the Hebrew wedding, the bride and the groom would make their vows, or their covenant to one another - they would become betrothed; and then the groom would go away, and he would prepare a place for his bride. Then, at the appointed time (she was aware of the time, but she wouldn’t know the exact time), he would return; and he would return at night, and would have with him his people, who had lamps, because it's dark. There were no streetlamps; the only light they have, is the one they're carrying. They would walk in a procession through the dark, come to the bride's home; and the bride is all prepared, all ready. She's got a lamp burning, and would accompany the groom, and they would go back into the wedding feast. The doors would be shut. That was the wedding feast.
In the wedding feast, it's a house, and it's full of light, it's full of life - it's the sound of music, of joy and laughter, the sound of a meal, and celebration. You're either: in the light of the wedding feast; or you're outside - and there's no light, you're in the outer darkness outside. So ‘outer darkness’ refers to the conditions outside the banquet hall, meaning exclusion from the celebration of the marriage feast.
You could only begin to imagine the grief of knowing that you were invited to something, but because you were unfaithful, careless and negligent - you're now disqualified! People who were in the same meeting with you, when you put your hand up to get saved - they got saved in the same meeting, and they're in there, but you are not! The devastation would be amazing!
That brings us to the next statement… “there will be weeping and gnashing of teeth” (verse 30). What does that mean? It's an expression that refers to two things...
1) The ‘weeping’ means deep sorrow, or grief, at the realisation of what I've lost. When we don't have a revelation of the importance of eternal rewards, there's no sense of urgency to grow, pursue Christ, and serve passionately. But there will come a time, when we will be aware what we've missed, and then there will be tremendous weeping - so the weeping refers to deep grief and sorrow.
2) The ‘gnashing of teeth’ refers to anger - it's an expression of anger. In Acts 7, it says they were angry or furious at Stephen, and they ‘gnashed their teeth’ on him. So, ‘gnashing of teeth’ refers to anger at being outside, when you really wanted to be inside. It's not then the suffering of hell; it's grief, sorrow, and anger at being excluded from the feast where there's laughing and celebration.
We could be near to Jesus, celebrating. Imagine being outside and hearing the joy - it's like being outside a party, and you hear all the fun, the laughter, people celebrating, the lights and music… but you're outside, and being excluded. Man, the feelings of grief and sorrow!
When Jesus returns to bring justice to the earth, to establish His kingdom, some Christians will experience His coming with great joy, gladness, and celebration. They were prepared, they were faithful, they enter in - and now, not only the celebration; they're now going to be acknowledged and given roles and responsibilities in the coming kingdom. Wow! The joy of that!
That's what keeps you going, moving forward, and persevering - the stakes are very high, and very eternal. Imagine then, other Christians experiencing shame, regret, sorrow, exclusion, exclusion for what they were called to be a part of. They were called, but they were not chosen, because they weren't faithful. How sad is that?
All believers need to develop a faithful and a loyal heart; and take what we have and use it to the best of ability that we can. There are other parables that talk about the basis for rewards - that's one of the very best ones. I encourage you to search through the Parable on the Pounds (or Menas), in Luke 19:11-27, where the focus there is not on equal faithfulness, equal reward. The focus in that one is that when someone is more diligent, they will gain more reward. This teaching is very clearly there to show to us the importance in our lives, of not just of being faithful, but also being diligent, to be productive for Him.