Why does the LDS church believe in Joseph Smith?
Forgive me if I am misunderstanding your question, but, you seem to be asking if members of the Church of Jesus Christ of Latter-day Saints worship Joseph Smith. I think President Gordon B. Hinkley spoke for all members of the church when he made the following statement regarding Joseph Smith:
“We do not worship Joseph Smith the Prophet. We worship God our Eternal Father and the risen Lord Jesus Christ. But we acknowledge the Prophet; we proclaim him; we respect him; we reverence him as an instrument in the hands of the Almighty in restoring to the earth the ancient truths of the divine gospel, together with the priesthood through which the authority of God is exercised in the affairs of His Church and for the blessing of His people”
Just as the Exodus story is inseparable from Moses, so too is the Restoration of the Gospel in the last days inseparable from Joseph Smith. Both were called to perform mighty labors and both are revered as prophets of the Almighty.
No, we do not worship Joseph Smith, but we do honor his memory and marvel at his great works. I echo the sentiment of the words of a beloved hymn:
” Praise to the man who communed with Jehovah!
Jesus anointed that Prophet and Seer.
Blessed to open the last dispensation,
Kings shall extol him, and nations revere.”