Moroni 10:32

Yea, come unto Christ, and be perfected in him, and deny yourselves of all ungodliness; and if ye shall deny yourselves of all ungodliness, and love God with all your might, mind and strength, then is his grace sufficient for you, that by his grace ye may be perfect in Christ; and if by the grace of God ye are perfect in Christ, ye can in nowise deny the power of God.

We are perfected, or completed, only by Christ. We cannot do it on our own. All the self-help books in the world cannot change us enough to meet God's standards. Only Jesus and the atonement and the power of the Holy Ghost can make the kind of changes in us that qualify as perfection.  We must try and do our best, but we must always remember where the power to please God comes from.

Moroni 10:19

And I would exhort you, my beloved brethren, that ye remember that he is the same yesterday, today, and forever, and that all these gifts of which I have spoken, which are spiritual, never will be done away, even as long as the world shall stand, only according to the unbelief of the children of men.

The logic of this verse is impeccable. God is always the same. He must be the same at all times, for he is perfect, and perfection is complete and unchanging. If perfection were to change, then it wasn't perfect to begin with, or it is no longer perfect now. If perfection is not absolute, then God is neither perfect nor absolute, and so he is no god at all. But if God is perfect and absolute, then he is unchanging. And being unchanging, he can do today what he did yesterday. In fact, he is guaranteed to keep doing the same things the same way because they are perfect. We either believe in a perfect, unchangeable God or we believe in no God at all. We either believe in gifts of the Spirit, revelation, and miracles today, or we believe they never existed. Any middle ground is simply illogical.

3 Nephi 18:29

For whoso eateth and drinketh my flesh and blood unworthily eateth and drinketh damnation to his soul; therefore if ye know that a man is unworthy to eat and drink of my flesh and blood ye shall forbid him.

Let's be clear: no one is worthy to partake of the sacrament. We come to the sacrament table in introspection and repentance, acknowledging that we failed to keep our covenants perfectly during the preceding week. We renew our covenants of the sacrament weekly because weekly we fall short of our desires to be faithful and righteous. Therefore, to partake worthily does not mean to be without sin but to be without hypocrisy. We partake worthily when we truly want to keep the covenants we make and are willing to strive to be obedient. The point of the sacrament is not to be perfect but to have the intent to become perfect through the continuous atonement of Christ.  Jesus warns his disciples about those who partake of the sacrament for show or to be socially acceptable or to hide rebellion and intentional sins. For such, the sacrament is a curse rather than a blessing. If one does not intend to keep the covenants, it is best that he not pretend to make them in the first place. For the rest of us, we just have to keep trying.

3 Nephi 12:48

Therefore I would that ye should be perfect even as I, or your Father who is in heaven is perfect.

Jesus commands us to be perfect. Now, we know that he gives no commandments unto the children of men save he prepare a way for them to keep the commandment with his help (see Nephi 3:7). We can therefore assume that he is ready to help us and that perfection is achievable. "Ask Heavenly Father to bless you with these attributes you cannot develop them without His help" (PMG p. 115).

What he does not give us in this commandment is a timeframe. He doesn't say when we have to reach perfection. He gives no deadline. It takes as long as it takes, and we each move along the path to perfection at our own pace. As long as we are striving to stay on the path and make progress through the grace of Christ, we are keeping this commandment. It does not matter whether we achieve the goal in this life or the next. We are judged by trajectory, not speed. We must have patience and not get discouraged and give up. Christ is in this with us for the long haul.

Enos 1:8

And he said unto me: Because of thy faith in Christ, whom thou hast never before heard nor seen. And many years pass away before he shall manifest himself in the flesh; wherefore, go to, thy faith hath made thee whole.

Faith in Christ, manifested by sincere and humble repentance, heals us. Not our works, not our callings, not our service, not our tithing, not our knowledge, and not our obedience. All are flawed. Only Christ is perfect. We cannot work enough, serve enough, pay enough, sacrifice enough, learn enough, or obey enough to earn our way into heaven. Not that working, serving, sacrificing, paying learning and obeying are not essential. They are simply not enough. They help change us and shape us. But only Jesus Christ, through his atonement, can make us fit for the kingdom of God. Only He can heal all the wounds others inflict on us, we inflict on others, and we inflict on ourselves. Only when we are healed are we fit to be in the Father's presence. He does not want us full of sores, He wants us perfect. Christ can make us perfect.

Second Nephi 27:23

For behold, I am God; and I am a God of miracles; and I will show unto the world that I am the same yesterday, today, and forever; and I work not among the children of men save it be according to their faith.

God does not change. What he did yesterday, he is doing today and will do again tomorrow. God cannot change and still be God. One cannot improve on perfection, and God is, by definition, perfect. If he changed, he would have to devolve from perfection, and thus he would cease to be God. Because God is perfect and unchanging, we can trust him. We can also expect certain things of him. If he used to speak to prophets, he will speak again. If he gave scriptures in the past, he will give us more scriptures now and in the future. If he created one world, he will create another. God's reality is one eternal round.