According to LDS doctrine, why are we created as spirits before we can receive a body? On earth, all creatures are born with the same bodies as their parents. In the preexistence, why are the children of God born/created out of different matter (spirits) than our heavenly parents? Our Father in Heaven is a physical being. If we are literal offspring of our Father in Heaven, then why aren't we born in the pre-earth life with a physical body, the same as our Father in Heaven?
Technically, we are not first created as spirits. This is a simplification. We existed as intelligences, which are not clearly explained, and later formed into our spirits by God.
Man was also in the beginning with God. Intelligence, or the light of truth, was not created or made, neither indeed can be. D&C 93:29
Speaking of this topic, Marion G. Romney has said:
In origin, man is a son of God. The spirits of men “are begotten sons and daughters unto God” (D&C 76:24). Through that birth process, self-existing intelligence was organized into individual spirit beings.
After that physical form was created to house the spirits.
Our bodies, my brethren, our minds, are the tabernacles of our spirits. - Gordon B. Hinkcley
By extension, it is reasonable to believe that all life also came from intelligences, which may not have been suited to become human. Therefore things are created or organized spiritually first, because without the spiritual existence there is no purpose in the physical creation.
For further reading, I recommend the article on Intelligences in the Encyclopedia of Mormonism
God is both spirit (John 4:24) and physical (Luke 24:37-39). Also, spirit beings (unembodied or disembodied) may be more physical than we realize. Joseph Smith taught, "There is no such thing as immaterial matter. All spirit is matter, but it is more fine or pure, and can only be discerned by purer eyes" (Doctrine & Covenants 131:7). Moreover, a careful read of the creation in Genesis suggests a spiritual and then a physical creation (https://rabbidaniellapin.com/the-chimp-and-i/).
God knew us before we were born here ( of water/woman).( Jeremiah 1:5; Psalm 82:3-4) We were formerly with him as his sons ( Angels/spirits). Jesus said "you must be born of water and the spirit to enter into the Kingdom of God."( John 3:5) A third of the Angels sinned and were removed, cast to earth. ( Ezekiel 28; Isaiah 14; Revelation 12:4) Our allotted time here is to 'run a good race and finish and return to our Father. (2 Timothy 4:7-8;,Ecclesiastes 3:21; 12:7; ) I think this life and time here is a time and place for testing; to come into relationship with our Heavenly Father and His Son, our brother Jesus. ( Mark 3:35)