Who ever said that in the Bible?
The prophet Amos wrote,
"Indeed, the Lord God does nothing
without revealing His counsel
to His servants the prophets." Amos 3:7
And reveal His plan He certainly did.
YHWH promised it in the very first Book of the Bible. Moses recorded this for us in Genesis 3:15 (italics mine),
"I will put hostility between you and the woman, and between your seed and her seed. He will strike your head, and you will strike his heel."
The prophet Isaiah said it in Isaiah 9:6,
"For a Child will be born for us, a Son will be given to us, and the government will be on His shoulders. He will be named Wonderful Counselor, Mighty God, Eternal Father, Prince of Peace."
The prophet Jeremiah said it in Jeremiah 23:5,
“The days are coming”—this is the Lord’s declaration— “when I will raise up a Righteous Branch of David. He will reign wisely as king and administer justice and righteousness in the land.”
Jeremiah said it again in Jeremiah 33:15,
"In those days and at that time I will cause a Righteous Branch to sprout up for David, and He will administer justice and righteousness in the land."
The prophet Zechariah said it in Zechariah 2:11,
“Many nations will join themselves to the Lord on that day and become My people. I will dwell among you, and you will know that the Lord of Hosts has sent Me to you."
The prophet Malachi said it in Malachi 3:1,
“See, I am going to send My messenger, and he will clear the way before Me. Then the Lord you seek will suddenly come to His temple, the Messenger of the covenant you desire—see, He is coming,” says the Lord of Hosts.”
John said it in John 1:
1 In the beginning was the Word, and the Word was with God, and the Word was God.
14 The Word became flesh and took up residence among us. We observed His glory, the glory as the One and Only Son from the Father, full of grace and truth.
Jesus Himself said it in John 3,
17 For God did not send His Son into the world that He might condemn the world, but that the world might be saved through Him.
The Apostle Paul said it in Philippians 2,
5 ... Christ Jesus,
6 who, existing in the form of God,
did not consider equality with God
as something to be used
for His own advantage.
7 Instead He emptied Himself
by assuming the form of a slave,
taking on the likeness of men.
And when He had come as a man
in His external form,
8 He humbled Himself by becoming obedient
to the point of death—
even to death on a cross.
John the Beloved tells us that whoever confesses that God has come in the flesh is of God in 1 John 4:
2 This is how you know the Spirit of God: Every spirit who confesses that Jesus Christ has come in the flesh is from God.
And finally, Jesus wraps it all up for us in Revelation 1:17-18,
“Don’t be afraid! I am the First and the Last, and the Living One. I was dead, but look—I am alive forever and ever, and I hold the keys of death and Hades.”
Why did YHWH do it?
As Jesus said in John 3:16,
“For God loved the world in this way: He gave His One and Only Son, so that everyone who believes in Him will not perish but have eternal life.”
God said it. That settles it. Believe it!