The Salt Lake Temple Dedication Plaque
The dedication plaque is located at the top of the east tower on the Salt Lake Temple. The gilded inscription carved into the stone wall reads:
Holiness to The Lord
The House of The Lord
Built by The Church of Jesus Christ of Latter-Day Saints
Commenced April 6, 1853
Completed April 6, 1893
Holiness to The Lord represents the inscription on the temples of the Old Testament, and was also inscribed on the crown of the high priest. (Exodus 28:36; Exodus 39:30) The inscription signifies the sanctity of the edifice, and acts as a reminder to exemplify Jesus Christ.
Jesus said, "Foxes have holes, and birds of the air have nests; but the Son of man hath not where to lay his head."(Luke 9:58) The inscription The House of the Lord is a symbol that identifies the temple as a house for Jesus Christ and Heavenly Father. The temple is a place for Him to lay His head.
The rest of the inscription is self-explanatory, it is the date construction on the temple was begun and completed. However, that date has other special significance. April 6, 1830, was the date that the Church of Jesus Christ of Latter-day Saints was officially organized and established. And according to LDS tradition, April 6th was the day Jesus was born.
Some people view the 40 years it took to complete the temple as analogous to the 40 years the children of Israel sojourned in the desert, waiting to enter in the Promised Land. After struggling, sacrificing and laboring for 40 years, the Saints were finally able to enter their promised land.
There's actually a very inspiring story that goes along with the Dedication Plaque. The words "Holiness to The Lord" were carved by John R. Moyle, a stone cutter who would walk 6 hours every morning from his home to work on the temple. He lost his leg in an accident, but continued to walk the whole distance on a pegleg. Watch a clip from a movie that portrays his story.