Doctrine and Covenants 93:33–34

Resurrection is necessary for us to receive a fulness of joy.

33 For man is spirit. The elements are eternal, and spirit and element, inseparably connected, receive a fulness of joy;
34 And when separated, man cannot receive a fulness of joy.

President Joseph F. Smith said:

“We are begotten in the similitude of Christ Himself. We dwelt with the Father and with the Son in the beginning, as the sons and daughters of God; and at the time appointed, we came to this earth to take upon ourselves tabernacles, that we might become conformed to the likeness and image of Jesus Christ and become like Him; that we might have a tabernacle, that we might pass through death as He has passed through death, that we might rise again from the dead as He has risen from the dead.”

(Teachings of Presidents of the Church: Joseph F. Smith 

[1998], 134.)