We use the phrase “washed white in the the blood of the lamb” rather loosely. I think I have even heard it used at baptisms. By contrast, the scriptures use it to refer to being sanctified and made holy (e.g. Moroni 10:32-33, Alma 13:11-12). I am suspicious that when we read that salvation was, and is, and is to come, in and through the atoning blood of Christ we fail to realize that what is being said is that salvation was, and is, and is to come by being washed white in the blood of the Lamb.
Mosiah 3:18 For behold he judgeth, and his judgment is just; and the infant perisheth not that dieth in his infancy; but men drink damnation to their own souls except they humble themselves and become as little children, and believe that salvation was, and is, and is to come, in and through the atoning blood of Christ, the Lord Omnipotent.
The point is that the issue of salvation is the issue of sanctification. Certainly baptism and the gift of the Holy Ghost set us on the path. We must be baptized by the water and the spirit. But our baptism is not yet a complete baptism, and, just like receiving the Holy Ghost, it is something that generally comes “many days” after we are baptized with water.
Moses 6:59 That by reason of transgression cometh the fall, which fall bringeth death, and inasmuch as ye were born into the world by water, and blood, and the spirit, which I have made, and so became of dust a living soul, even so ye must be born again into the kingdom of heaven, of water, and of the Spirit, and be cleansed by blood, even the blood of mine Only Begotten; that ye might be sanctified from all sin, and enjoy the words of eternal life in this world, and eternal life in the world to come, even immortal glory;
60 For by the water ye keep the commandment; by the Spirit ye are justified, and by the blood ye are sanctified;
61 Therefore it is given to abide in you; the record of heaven; the Comforter; the peaceable things of immortal glory; the truth of all things; that which quickeneth all things, which maketh alive all things; that which knoweth all things, and hath all power according to wisdom, mercy, truth, justice, and judgment.
62 And now, behold, I say unto you: This is the plan of salvation unto all men, through the blood of mine Only Begotten, who shall come in the meridian of time.
What is the plan of salvation? The plan of salvation came through the blood of his only begotten. The plan of salvation has not fully taken its proper place in our lives until we are washed white in his blood, even if that takes place in our old age, for by the water we keep the commandment, by the spirit we are justified, and by the blood we are sanctified.
Joseph Smith said that a man might as well baptize a bag of sand as baptize a man without being done in view of obtaining remission of sins and the Holy Ghost. And apparently, you may as well baptize a bag of sand as baptize a man if it isn’t done in view of his eventually receiving the Holy Ghost in earnest, proving that he is willing to follow God at all hazards, and being washed white by the blood of Christ which sanctifies.
What does it mean that we are to believe that salvation was, and is, and is to come, in and through the atoning blood of Christ, the Lord Omnipotent? It means that we are to believe that baptism by water and by the spirit is only half a baptism, and that both must be done in view of proving that we will follow God at all hazards that we may be washed white and sanctified by the blood of Christ.