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. The oil is the Holy Spirit that comes into man's spirit by the new birth that relights humankind. The Holy Spirit cannot be purchased. The human spirit needs The Holy Spirit. The Holy Spirit is the light in the lamp of mankind's redeemed spirit.