Concerning the history of the unfaithfulness of Israel Paul writes...
“Now these things happened to them as an example, and they were written for our instruction, upon whom the ends of the ages have come.” (1 Corinthians 10:11)
The promises to ISRAEL that were dependent on their faithfulness needed to be exchanged for a covenant based on the faithfulness of sinless Jesus, rather than sinful humans.
"Now He has obtained a more excellent ministry, inasmuch as He is also Mediator of a better covenant, which was established on better promises.” (Hebrews 8:6)
The basic promises of the old covenant Law of Moses can be summarized as "do this, and you will live." The promises under the law were not realized because humanity does not obey the Law of God.
"Notwithstanding, the children rebelled against me; they did not walk in my statutes, and were not careful to observe my judgments, which, if a human does, he shall live by them" (Ezekiel 20:21).
God has promised a new covenant which is immeasurably better than the old one, because it DOES NOT depend upon human performance, but on the GRACE of God.
"I will make a new covenant… I will put my law in their minds…I will be their God…I will forgive their iniquity, and their sin I will remember no more." (Jeremiah 31:31-34)
What God has promised to forgive the iniquity of humanity and remember our sins no more! Paul was given this good news to tell everyone.
“For this is good and acceptable in the sight of God our Savior; who will have ALL humanity to be saved, and to come unto the knowledge of the truth. For there is one God, and one MEDIATOR between God and humans, the man Christ Jesus; who gave Himself a ransom for ALL, to be testified in due time. Whereunto I am ordained a preacher, and an apostle, I speak the truth in Christ, and lie not ; a teacher of the Gentiles in faith and verity.” (1 Timothy 2:3-7)