President Joseph Fielding Smith observed: “I believe the Lord meant just what he said: that we should be perfect, as our Father in heaven is perfect. That will not come all at once, but line upon line, and precept upon precept, example upon example, and even then not as long as we live in this mortal life, for we will have to go even beyond the grave before we reach that perfection and shall be like God.
“But here we lay the foundation. Here is where we are taught these simple truths of the gospel of Jesus Christ, in this probationary state, to prepare us for that perfection. It is our duty to be better today than we were yesterday, and better tomorrow than we are today. Why? Because … if we are keeping the commandments of the Lord, we are on that road to perfection, and that can only come through obedience and the desire in our hearts to overcome the world.
“… It is the duty of every man to try to be like his Eternal Father.
via LDS.org – Ensign Article – Prophetic Enlightenment on the Sermon on the Mount.