A Christian must believe that…

Jesus Christ is THE Son of God in a sense no other man is—the only begotten of the Father—not that He is A Son of God in the sense all men are.

Geneses 3: 15

15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.

Isaiah 7:14

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.

Isaiah 9:6-7

6 For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counselor, The mighty God, The everlasting Father, and The Prince of Peace.

7 Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. The zeal of the LORD of hosts will perform this.

Luke 1:34-35

34 Then said Mary unto the angel, how shall this be, seeing I know not a man?

35 And the angel answered and said unto her, The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that holy thing which shall be born of thee shall be called the Son of God.

John 1:18

18 No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared him.

John 3:16

16 For God so loved the world that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.