When Jesus washed His disciples feet He instituted an ordinance which He required Joseph Smith to also do. 

“By washing His Apostles’ feet, the Savior not only performed a beautiful act of service, but He also fulfilled a part of the law of Moses and instituted a sacred ordinance to help His faithful followers become clean from sin. This ordinance was restored in our dispensation through the Prophet Joseph Smith.” (source)

The Savior commanded Joseph in Doctrine and Covenants 88:139 to participate in this ordinance. “And ye shall not receive any among you into this school [School of the Prophets] save he is clean from the blood of this generation; And he shall be received by the ordinance of the washing of feet, for unto this end was the ordinance of the washing of feet instituted.”

Why did this ordinance exist? Apart from the symbolism of becoming clean, “It is calculated to unite our hearts, that we may be one in feeling and sentiment, and that our faith may be strong, so that Satan cannot overthrow us, nor have any power over us here.” – Joseph Smith (History of the Church, Vol 2, 308-9)”

This ordinance still exists in our day! “The ordinance of washing of the feet has now been incorporated in the ordinances that are revealed to be administered in the Lord’s house.” Companion to Your Study of the Doctrine and Covenants, Volume 2, Dr. Daniel H. Ludlow