I am going to give you the Reformed understanding of soteriology, I will try to be precise as to not make the post too lengthy so that you type "TLDR".
God, in His foreknowledge (and His foreknowledge is not merely Him knowing ahead of time but it is a Greek verb, meaning He did something in this foreknowing) knew about the fall, and had the plan already in place to remedy that fall. After the fall, God gave the first prophecy, the first proclamation of the gospel when He said to the Serpent, "And I will put enmity between you and the woman, and between your seed and her seed; He shall bruise you on the head, and you shall bruise him on the heel.”[Genesis 3:15] Here we see a clear line of demarcation between the sheep and goat, the elect and non-elect. Both sides agree there are two groups I just mentioned, but both arrive at the same conclusion via different means. Later we see that the world is completely wicked when we read, Then the Lord saw that the wickedness of man was great on the earth, and that every intent of the thoughts of his heart was only evil continually.[Genesis 6:5] Here God could have justly condemned the whole Adam race and completely wiped them (us) out, but we can take comfort in these words, But Noah found favor in the eyes of the Lord.[Genesis 6:5] Noah found favor (grace in the KJV, iirc, when means unmerited favor), so Noah was no better in the sight of God than the rest, but he (Noah) found favor in God's sight.
There were eight souls saved during the flood and then later we see God coming to Abram, who was an idol worshiper in Ur of the Chaldees. God makes him a promise that he would make him the father of many nations, and that the number of his seed was as much, if not more, than the sand on the seashores and the stars in the sky. Later Joseph gets sold into slavery and makes his way up to next in command to Pharoah, and Jacob and his family, along with their livestock move to Egypt and survive the drought and famine. Eventually another Pharoah rises to the throne who knew nothing of Joseph and that Pharoah and evil entreats the ppl of God and He sends them Moses and Aaron to deliver them out of Egypt.
God later says these words that show those He chose was based solely upon Himself and nothing inherently good within them, "For you are a holy people to the Lord your God; the Lord your God has chosen you to be a people for His own possession out of all the peoples who are on the face of the earth. The Lord did not set His love on you nor choose you because you were more in number than any of the peoples, for you were the fewest of all peoples, but because the Lord loved you and kept the oath which He swore to your forefathers, the Lord brought you out by a mighty hand and redeemed you from the house of slavery, from the hand of Pharaoh king of Egypt."[Deuteronomy 7:6-8] And to further drive home this point, He said “You only have I chosen among all the families of the earth;.”[Amos 3:2a] So, God has always been a particular God to a particular ppl.
God choosing Israel based solely upon Himself and absolutely nothing from them, mirrors His electing grace in the NT. The elect are the elect based solely upon Him, not them. There was not something special in them that was missing in the non-elect, nor were the non-elect more wicked than the non-elect, and that caused Him to choose them.
And this story is replete in both Testaments.
