In one of my favorite conference talks ever given Elder Russell M. Nelson explained his thoughts on perfection and how it is not exactly what we probably think it is in this life. An excerpt of passages from his talk is found below and the full version (which should be read in its entirety) is found here.
When you follow the link to lds.org make sure to read the footnotes of this talk as well as they provide additional insights into the original Greek derivations of "perfect."
"If I were to ask which of the Lord’s commandments is most difficult to keep, many of us might cite Matt. 5:48: “Be ye therefore perfect, even as your Father which is in heaven is perfect.” 1
When comparing one’s personal performance with the supreme standard of the Lord’s expectation, the reality of imperfection can at times be depressing. My heart goes out to conscientious Saints who, because of their shortcomings, allow feelings of depression to rob them of happiness in life.
We all need to remember: men are that they might have joy—not guilt trips! 2 We also need to remember that the Lord gives no commandments that are impossible to obey. But sometimes we fail to comprehend them fully.
James gave a practical standard by which mortal perfection could be measured. He said, “If any man offend not in word, the same is a perfect man.” 4
Scriptures have described Noah, Seth, and Job as perfect men. 5 No doubt the same term might apply to a large number of faithful disciples in various dispensations. Alma said that “there were many, exceedingly great many,” 6 who were pure before the Lord.
This does not mean that these people never made mistakes or never had need of correction. The process of perfection includes challenges to overcome and steps to repentance that may be very painful. 7 There is a proper place for chastisement in the molding of character, for we know that “whom the Lord loveth he chasteneth.” 8
But Jesus asked for more than mortal perfection. The moment he uttered the words “even as your Father which is in heaven is perfect,” he raised our sights beyond the bounds of mortality. Our Heavenly Father has eternal perfection. This very fact merits a much broader perspective.
Recently I studied the English and Greek editions of the New Testament, concentrating on each use of the term perfect and its derivatives. Studying both languages together provided some interesting insights, since Greek was the original language of the New Testament.
In Matt. 5:48, the term perfect was translated from the Greek teleios, which means “complete.” Teleios is an adjective derived from the noun telos, which means “end.” 10 The infinitive form of the verb is teleiono, which means “to reach a distant end, to be fully developed, to consummate, or to finish.” 11 Please note that the word does not imply “freedom from error”; it implies “achieving a distant objective.” In fact, when writers of the Greek New Testament wished to describe perfection of behavior—precision or excellence of human effort—they did not employ a form of teleios; instead, they chose different words. 12
Teleios is not a total stranger to us. From it comes the prefix tele- that we use every day. Telephone literally means “distant talk.” Television means “to see distantly.” Telephoto means “distant light,” and so on.
With that background in mind, let us consider another highly significant statement made by the Lord. Just prior to his crucifixion, he said that on “the third day I shall be perfected.” 13 Think of that! The sinless, errorless Lord—already perfect by our mortal standards—proclaimed his own state of perfection yet to be in the future. 14 His eternal perfection would follow his resurrection and receipt of “all power … in heaven and in earth.” 15
The perfection that the Savior envisions for us is much more than errorless performance. It is the eternal expectation as expressed by the Lord in his great intercessory prayer to his Father—that we might be made perfect and be able to dwell with them in the eternities ahead. 16
The Lord’s entire work and glory pertains to the immortality and eternal life of each human being. 17 He came into the world to do the will of his Father, who sent him. 18 His sacred responsibility was foreseen before the creation 19 and was foretold by all his holy prophets since the world began. 20
The atonement of Christ fulfilled the long-awaited purpose for which he had come to the earth. His concluding words upon Calvary’s cross referred to the culmination of his assignment—to atone for all humankind. Then he said, “It is finished.” 21 Not surprisingly, the Greek word from which finished was derived is teleios.
That Jesus attained eternal perfection following his resurrection is confirmed in the Book of Mormon. It records the visit of the resurrected Lord to the people of ancient America. There he repeated the important injunction previously cited but with one very significant addition. He said, “I would that ye should be perfect even as I, or your Father who is in heaven is perfect.” 22 This time he listed himself along with his Father as a perfected personage. Previously he had not. 23
Our climb up the path to perfection is aided by encouragement from the scriptures. They hold the promise that we shall, if faithful in all things, become like Deity. John the beloved Apostle wrote:
“We should be called the sons [and daughters] of God. …
“… When he shall appear, we shall be like him; for we shall see him as he is.
“And every man that hath this hope in him purifieth himself, even as he is pure.” 33
Continuing encouragement comes as we follow the example of Jesus, who taught, “Be ye holy; for I am holy.” 34 His hope for us is crystal clear! He declared: “What manner of men ought ye to be? Verily I say unto you, even as I am.” 35 Thus, our adoration of Jesus is best expressed by our emulation of Jesus. 36 "
Russell M. Nelson, “Perfection Pending,” Ensign, Nov 1995, 86