Five wise virgins had been prepared for the late hour arrival with additional oil, but five foolish virgins were not prepared. When the Bridegroom arrived it was at that point that the differences of the virgin Bridesmaids were exposed. The foolish virgins were ultimately denied access to the wedding feast and they sought to enter but could not. It was oil that made some virgins wise and the lack of oil that made some foolish. Absence of oil indicates lack of salvation.
Oil is a symbol of The Holy Spirit.
The Bridegroom is Christ the Lord and King at His Second return. The Lord Jesus Christ is portrayed as the husband of His people. The time of delay is used as a time of testing. Midnight is a symbol of the end of the era. The lamp represents the spirit of man, and the lamp needs oil.