God had already planned His blueprint of creation that the Son
of God, Jesus Christ was to come to the world to accomplish God's redemptive plans (the Gospel). The Bible, thus tells us that salvation through Christ is not the means of solution added later as the result of man's sin.
Some might be surprised by this fact. Paul, one of Jesus' apostle
says that all things were created by Him and for Him. This amazing declaration that God has predestined everything is written everywhere in the Bible.

Luke,who was the only gentile author in the Bible says,

this is how God fulfilled what he had foretold
through all the prophets,
saying that his Christ would suffer.

The first prophecy that Jesus would come for the salvation of the
world is already written in Genesis shortly after Adam and Eve
sinned (that is, they did not obey God's command). God declared war
against Satan:

I will put enmity between you and the woman,
and between your offspring and hers;
he will crush your head, and you will strike his heel.

He has prophesied that the one who brings victory over Satan would appear out of Jewish offspring, that is, Jesus' victory on the cross.
Satan's struggle with God in order to hinder God's children from
eternal salvation for the short while, when he is allowed to have
power and to rule over the world explains why human history has
been bloodshed by atrocities such as the holocaust and the massacre of infants.

Col.1:16
Is.14:24,46:9-11,48:3-5, Ac.2:23,4:28, Ep.1:4-5,:11
Ac.3:18
Ge.3:15

Thus, God has progressively been revealing His unchanging plans
from the beginning of His creation through His covenants with
Abraham, with Moses, with David and with the Israelites and also
through revelations and visions to Israel's patriarchs, leaders kings
and many Old Testament prophets such as Isaiah, Jeremiah, Ezekiel,
and so on in different ages.
These prophecies written in the Hebrew Bible testify that Jesus Christ came to the world as a human (incarnated) 2000 years ago
and is also to come back again. Therefore, Jesus Christ, that is, the New Testament, written about Christ after His first coming, can be
described to interpret the Hebrew Bible which had already been
written by then. In other words, the New Testament tells us that
Christ is the very one that fulfils what is written in the Hebrew
Bible.
Jesus, Himself taught that the Hebrew Bible could be understood
in the light of the gospel. Furthermore the author of the Epistle to
the Hebrews in the New Testament also tells us that God's promises have been embodied in Jesus Christ, saying,

In the past God spoke to our forefathers through the prophets
at many times and in various ways,
but in these last days
he has spoken to us by his Son.

Indeed, it is no other than the sinless Son of God, Jesus Christ who can achieve the redemptive plans of God who is both love and righteous and whose plans are even to save a sinful man without
violating God's law which is described in detail in the Hebrew Bible.

Ge.12:2-7
Ex.19:5-6
2Sa.7:14-16, 1Ch.17:4-14
Jer.31:31-34, Eze.36:24-29
Lk.24:27,:44-49 Jn.5:39,:46
Heb.1:1-2