The prophets in the Old Testament spoke often of the coming Messiah and that he would be the Son of God.
In Chronicles 17, the LORD told Nathan the prophet to tell David:
11 And it shall come to pass, when thy days be expired that thou must go to be with thy fathers, that I will raise up thy seed after thee, which shall be of thy sons; and I will establish his kingdom.
12 He shall build me an house, and I will stablish his throne for ever.
13 I will be his father, and he shall be my son: and I will not take my mercy away from him, as I took it from him that was before thee:
14 But I will settle him in mine house and in my kingdom for ever: and his throne shall be established for evermore.
Then in the New Testament, when asked about Jesus in John 3, John the Baptist said:
30 He must increase, but I must decrease.
31 He that cometh from above is above all: he that is of the earth is earthly, and speaketh of the earth: he that cometh from heaven is above all.
32 And what he hath seen and heard, that he testifieth; and no man receiveth his testimony.
33 He that hath received his testimony hath set to his seal that God is true.
34 For he whom God hath sent speaketh the words of God: for God giveth not the Spirit by measure unto him.
35 The Father loveth the Son, and hath given all things into his hand.
36 He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.
And finally, the words of Jesus himself in John 17:
1 These words spake Jesus, and lifted up his eyes to heaven, and said, Father, the hour is come; glorify thy Son, that thy Son also may glorify thee:
2 As thou hast given him power over all flesh, that he should give eternal life to as many as thou hast given him.
3 And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.
No one finds eternal life with the Father until they first believe in his Son. May we each put our complete trust and faith in the Son of God, the Living God, the Lord Jesus Christ. "Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me."