Both the Bible (Matthew 1:18), and the Book of Mormon (Alma 7: 10) teach that Jesus was conceived by the power of the Holy Ghost.
Neither the Bible nor the Book of Mormon teach that Heavenly Father had physical sexual relations with Mary like the
LDS prophets teach. Jesus was conceived through the power of the Holy Ghost ... and not through a physical aspect like LDS teaches.
Plus, if Mary had physical sexual relations with Heavenly Father, she would not be a virgin any more. According to the Book of Mormon,
Nephi has a vision in which the virgin Mary is holding the baby Jesus in her arms ... after he's born ... See 1 Nephi (11:18-21).
Since LDS teaches that Mary had physical sexual relations with Heavenly Father, Mary cannot be a virgin like 1 Nephi (11:18-21)
says. Impossible.
Look at Isaiah (7:14) - "Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, AND bear a son, and
shall call his name Immanuel. The sign is that a virgin gave birth to a son. A non-virgin
giving birth is not a sign but rather a natural occurrence.
And the birth of Christ was a supernatural sign.
But the LDS prophets taught (and the verses below) that Heavenly Father had literal and physical sexual intercourse
with Mary to create Jesus just like wives and husbands procreate to have their children.
LDS prophets reject any involvement of the Holy Ghost.
Let us examine their teachings:
Brigham Young, second prophet and president of the LDS church said, "The birth of the Saviour was as natural as are the births of our
children; it was the result of natural action. He partook of flesh and blood-was begotten of his Father, as we were of our fathers."
(Journal of Discourses, v. 8, p. 115).
Brigham Young also said, "Now, remember from this time forth, and for ever, that Jesus Christ was not begotten by the Holy Ghost."
(Journal of Discourses, Vol. 1, page 51).
Joseph Fielding Smith, stated: "The birth of the Savior was a natural occurrence unattended with any degree of mysticism, and
the Father God was the literal parent of Jesus in the flesh as well as in the spirit." (Religious Truths Defined, p. 44).
Joseph Fielding Smith said, "They tell us the Book of Mormon states that Jesus was begotten of the Holy Ghost. I challenge
that statement. The Book of Mormon teaches no such thing. Neither does the Bible." (Doctrines of Salvation, Vol. 1, page 19)
Bruce McConkie, who was a member of the First Council of the Seventy stated, "Christ was begotten by an Immortal Father in
the same way that mortal men are begotten by mortal fathers," (Mormon Doctrine, 1966, page 547.) "And Christ was born into
the world as the literal Son of this Holy Being; he was born in the same personal, real, and literal sense that any mortal son
is born to a mortal father. There is nothing figurative about
his paternity; he was begotten, conceived and born in the normal and natural course of events,...Christ is the Son of Man,
meaning that his Father (the Eternal God.) is a Holy Man." (Mormon Doctrine, by Bruce McConkie, page 742.).
It is these Biblical truths that Mormons reject.