Having trusted God and come to mortality, those who come to Christ are learning to live by faith in him, trusting that he can make us otherwise than we are. As we live by faith, the way in which we see and experience the world changes; we repent. And as we live repentant lives, in principle our fallen state is overcome: we return to a direct relationship with God if we welcome the Holy Spirit.
The assurance given to those who welcome him is extraordinary. Doctrine and Covenants 121:41-46 promises that if we exercise whatever supposed authority we may have over others "by persuasion, by longsuffering, by gentleness and meekness, and by love unfeigned," and if we let our "bowels also be full of charity towards all men," and if we allow "virtue [to] garnish [our] thoughts unceasingly," then, "the Holy Ghost shall by [our] constant companion."
All those "ifs" seem of-a-piece to me: to exercise authority by persuasion, longsuffering, gentleness, and meekness requires that I have charity. Those things are charity. And I cannot have charity for anyone if the center of my being is not strengthened and supplied—garnished—with moral excellence in the broadest sense, the excellence of God. Being loving as God is and being morally good are the same thing.
Living in God's presence in mortality, in other words having the Holy Spirit, doesn't mean power, will, and vainglory. It means meekness, love, and moral excellence. That's the newness of life toward which the commandment to receive the Holy Ghost leads us. Welcoming the Holy Ghost is the culmination of faith, repentance, and baptism.