...I do not even believe that there is a single revelation, among the many God has given to the Church, that is perfect in its fulness. The revelations of God contain correct doctrine and principle, so far as they go; but it is impossible for the poor, weak, low, groveling, sinful inhabitants of the earth to receive a revelation from the Almighty in all its perfections. He has to speak to us in a manner to meet the extent of our capacities. . . .
If an angel should come into this congregation, or visit any individual of it, and use the language he uses in heaven, what would we be benefited? Not any, because we could not understand a word he said. When angels come to visit mortals, they have to condescend to and assume, more or less, the condition of mortals, they have to descend to our capacities in order to communicate with us. I make these remarks to show you that the kingdom of heaven is not yet complete upon the earth. Why? Because the people are not prepared to receive it in its completeness, for they are not complete or perfect themselves.
The laws that the Lord has given are not fully perfect, because the people could not receive them in their perfect fulness; but they can receive a little here and a little there, a little today and a little tomorrow, a little more next week, and a little more in advance of that next year, if they make a wise improvement upon every little they receive; if they do not, they are left in the shade, and the light which the Lord reveals will appear darkness to them, and the kingdom of heaven will travel on and leave them groping. Hence, if we wish to act upon the fulness of the knowledge that the Lord designs to reveal, little by little, to the inhabitants of the earth, we must improve upon every little as it is revealed.
-Journal of Discourses, 2:314