As long, therefore, as we are upon earth, let us practice repentance, for we are as clay in the hand of the artificer. For as the potter, if he make a vessel, and it be distorted or broken in his hands, fashions it over again; but if he have before this cast it into the furnace of fire, can no longer find any help for it: so let us also, while we are in this world, repent with our whole heart of the evil deeds we have done in the flesh, that we may be saved by the Lord, while we have yet an opportunity of repentance. For after we have gone out of the world, no further power of confessing or repenting will there belong to us. Wherefore, brethren, by doing the will of the Father, and keeping the flesh holy, and observing the commandments of the Lord, we shall obtain eternal life. For the Lord saith in the Gospel, "If ye have not kept that which was small, who will commit to you the great? For I say unto you, that he that is faithful in that which is least, is faithful also in much." 
This, then, is what He means: "Keep the flesh holy and the seal undefiled, that ye 
may receive eternal life."