The purpose of this article is to explain why …
There is a big difference between the Old Testament and New Testament.
There is a big difficulty in believing Jesus' gospel (good news).

Scripture verses back up all of the points below.

The OLD Testament (Covenant)
Almighty God introduced Himself to man, and He displayed some of His attributes.
This is an understandable historical account (except maybe for the miracles).
God chose the small and weak nation of Israel to be His "chosen people".
They were to represent mankind in God's interactions with man.
He gave them every opportunity to be successful in following and pleasing Him.
He repeatedly proved Himself to them through His mighty miracles.
He gave them His Commandments, which He warned were necessary to follow.
He gave them a salvation plan (repentance and blood sacrifices to cover their sins).
But, they really didn't understand (historically man has always been a spiritual idiot).
And they repeatedly disobeyed, rebelled, and sinned against God and His Law.
They proved forever (to everyone) that man is not capable of satisfying a Holy God.
Man's sins far outweigh his good deeds (a few sins would disqualify him anyway).
After many years, God had had enough, and He scattered His chosen people to the
4 corners of the earth, but promised to bring them back home at a later time (1948).
He had made His point, and here is the key to the whole matter:
God proved that man is totally incapable of satisfying a Holy God,
and no human is acceptable to spend eternity with Him in Heaven.
So, the fact is … man is doomed to always be separated from God.
Man's only hope would be for God to really intervene on his behalf.
So, He promised to introduce a new improved covenant which would satisfy Him.

The NEW Testament (Covenant)
God designed a plan of salvation that would save some of His creation.
(Certainly, some is a whole lot better than none.)
Note: As in the OT, Jesus also presented an impossible Law for man to follow.
God's plan consisted of 2 parts:
PART-1
He would choose and call His "elect" (those who He desired to save).
He would give them the gift of faith, and then give them to Jesus.
They would now be enabled to believe Jesus' gospel,
and they would be born again and given the Holy Spirit.
The "non-elect" would see Jesus' gospel as total foolishness.
This was done on purpose so they would not believe it.
God insisted on being in control; He didn't want just anyone believing it.
This whole plan was to be performed by Him, through Him, and for Him.
PART-2
He would sanctify (set apart) His "elect" and make them holy.
The Holy Spirit is placed "in" them, and stays "forever" (until their death).
He guides and teaches them, and makes it possible for them to overcome sin.
Jesus warned 7 times that only the overcomers will go to Heaven (Revelation 2-3).
Note: It is not possible to really understand the NT without the Holy Spirit's help.

If you find yourself questioning what God says and does … beware …
"For My thoughts are not your thoughts, nor are your ways My ways", says the Lord.
"For as the heavens are higher than the earth, so are My ways higher than your ways,
and My thoughts than your thoughts." (Isaiah 55:8-9)