“Not everyone who says to Me, ‘Lord, Lord,’ will enter the kingdom of heaven, but he who does the will of My Father who is in heaven will enter. Many will say to Me on that day, ‘Lord, Lord, did we not prophesy in Your name, and in Your name cast out demons, and in Your name perform many miracles?’ And then I will declare to them, ‘I never knew you; depart from Me, you who practice lawlessness.’ (Matthew 7:21-23)
Is this about judgment day or is it about the day (period of time) after Jesus' resurrection?
Jesus said in Luke 17:21, "Look, the kingdom of God is in your midst." This could easily picture Jews or anyone else who tries to "enter the kingdom" by their works. The will of the Father is to trust Jesus (John 6:40). We don't enter the kingdom upon the death of our flesh. We enter it when we are first saved. Likewise people try to enter the kingdom in the flesh by boasting of their own works. I think it teaches a more valuable & more urgent lesson this way than if it were about hell. Works don't get you into the kingdom, only trusting God to know Him does.