How did God prepare us for salvation?

Our Salvation was Foreordained

After the Fall, man had to be saved from His separation from God. He needed to find his way back to the Kingdom of God and to be freed from the suffering caused by disease and death and his sinful actions towards others on earth.

Why did God want to save mankind? God had no necessity to save mankind. It is because God made man out of His Love. He has endless mercy. God in the foreknowledge of the fall of man, foreordained our salvation, even before the foundation of the world (Eph 1:4). He knew we would fall and that this was part of a large plan to bring man in union with Him in true love as He loves His creation. In Scripture the Savior is called the Lamb of God and was foreordained before the foundation of the world (1 Peter 1:20). The Lord never abandoned us. The moment of man’s fall into sin, He led us toward our future salivation.

The Lord chose from the descendants of Noah, who had been saved from the Flood, a single race for the preservation of piety and faith in the one true God. (Race of Abraham, Isaac and Jacob, and the whole Hebrew people). He led them out of slavery in Egypt. He made a covenant with them. He sent them Judges and Prophets, warned them and chastised them and led them out of Babylonian captivity. He also prepared a very special person to become the Mother of the Son of God.

There were the Prophesies.

Moses proclaimed, The Lord your God will raise up for you a Prophet like me from your midst, from your brethren. Him you shall hear. (Deut. 18:15)

The words of Jesus himself echo this prophecy, For if you believed Moses, you would believe Me; for he wrote about Me. (John 5:46)
Psalm 21 was recognized by ancient rabbis as a hymn of the Messiah. See also Psalms 39,68, 108, 40, 15, 8)

Prophet Isaiah prophesied:

Who has believed our report? And to whom has the arm of the Lord been revealed for He shall grow up before Him as a tender plant, and as a root out of dry ground. He has no form or comeliness; and when we see Him, there is no beauty that we should desire Him. He is despised and rejected by men, a Man of sorrows and acquainted with grief. And we hid, as it were, our faces from Him; He was despised, and we did not esteem Him. Surely He has borne our griefs And carried our sorrows; yet we esteemed Him stricken, smitten by God, and afflicted. But He was wounded for our transgressions, He was bruised for our iniquities; the chastisement for our peace was upon Him, and by His stripes we are healed. All we like sheep have gone astray; we have turned, every one, to his own way; and the Lord has laid on Him the iniquity of us all. He was oppressed and He was afflicted, yet He opened not His mouth; He was led as a lamb to the slaughter, and as a sheep before its shearers is silent, so He opened not His mouth.  He was taken from prison and from judgment, and who will declare His generation? For He was cut off from the land of the living; for the transgressions of My people He was stricken… And He was numbered with the transgressors, and He bore the sin of many, and made intercession for the transgressors. (Is 53:1-8, 12)

By the time of Christ, the coming of the Messiah was anticipated. We can see this from the dialogue Jesus had with the Samaritan woman. I know that Messiah cometh, which is called Christ: when He is come, He will tell us all things (John 4:25) Paul also affirms the expectation. When the fullness of the time had come, God sent forth His Son (Gal 4:4)

God prepared the right conditions for the time of our Salvation. The Son of God was sent when the human race, following after Adam, had tasted in full, spiritually speaking, of the tree of knowledge and of good and evil, and had come to know in experience the sweetness of doing good and the bitterness of evil-doing; when for the most part mankind had reached an extreme degree of impiety and corruption; when the best, although smallest, part of humanity had an especially great thirst, longing, and desire to see the promised Redeemer, Reconciler, Savior, Messiah; when, finally, by God’s will, the political conditions were ready because the whole of the civilized part of humanity had been united under the authority of Rome - something which strongly favored the spreading of faith and the Church of Christ. Then the promised and expected Son of God came to earth.
Great is the mystery of godliness: God was manifest in the flesh (1 Tim 3:16)