Jesus used the phrase "weeping and gnashing" on five different occasions in the Bible. It is a prophetic warning about the pain, the anger, the sorrow, the regret, the remorse and the sense of loss that will be felt on getting into heaven without being ready for it.
All those who end up weeping and gnashing their teeth would have missed out on the eternal rewards they could have had in heaven! They will miss the joy they could have had and they will miss the crowns of glory.
Renowned author, Dag Heward-Mills in his usual unequivocal style, describes the frightening reality of how many will regret the lost opportunities while on earth. You must do whatever you can to avoid becoming one of the people who will be weeping and gnashing their teeth in regret!