"Seventh Day Adventists, in reverse of Ambrose, believe baptism represents justification once and for all, and foot washing, ongoing sanctification." ChristianHistory
As an SDA, I've never heard that before. Maybe the church holds that position, that the symbolism of baptism is representative of justification & that foot washing is symbolic of sanctification. But then again, maybe the church doesn't hold to that. But I've never heard that stated in the church.
Either way though, the concept isn't a salvation issue---so believe what you want about what the foot washing and baptism are symbolic of....
Peter saith unto him,
Thou shalt never wash my feet.
Jesus answered him,
If I wash thee not,
thou hast no part with me.
John 13:8
"The whole life of Christ had been a life of unselfish service. 'Not to be ministered unto, but to minister' (Matt. 20:28) had been the lesson of His every act. But not yet had the disciples learned the lesson. At this last Passover supper, Jesus repeated His teaching by an illustration that impressed it forever on their minds and hearts". The Desire of Ages, p. 642 E.G.W.
"The washing of one another's feet is an act of loving dedication to one's partner, who is also a representative of all humanity, of our willingness to do for that one whatever may be necessary, even to the point of death. When we take the feet of our brother or sister in our hands and wash them, we are saying to him or her, "I love you as a brother or sister in Christ, and you can count on me to be of service to you, however humble it may be, even to the point of giving my life for you." Unless one enters into it in this spirit, prepared to make this commitment, it cannot be said that one has truly taken part in the service and has "washed one another's feet."
AdventistReview