Belief opens the door to God's kingdom.
Now after John was put in prison, Jesus came to Galilee preaching the gospel of the kingdom of God and saying, “The time is fulfilled and the kingdom of God is at hand. Repent and believe in the gospel.” (Mark 1:14-15 NKJV)
Jesus' gospel of the kingdom is the gospel of grace by which a person enters God's family.
That passage is in Mark 1 - some three and a half years or so before He was crucified.
Say you're a 1st Century Jew. All your life you've heard the Law and the Prophets assert that one day the God of your fathers will send a Messiah to deliver your people from their enemies and restore your kingdom under David back to you.
He shows up in your lifetime - three and a half years from His death and resurrection - something you know nothing about as you left your time machine at home.
Anyway, He shows up announcing "The time is fulfilled and the kingdom of God is at hand. Repent and believe in the gospel.”
Do you react with, "oh cool, Jesus died for my sins, oh, okay, I believe the gospel that Jesus died for my sins; halleluiah, praise the Lord, oh how I love Jesus and the Bible!"
Or, do you "repent" - change your mind about the God of your fathers they long ago turned their backs on - turn back to Him and "believe the gospel" - being announced by this Jesus - the good news - that "the time is fulfilled, and the kingdom of heaven is at hand."
Problem is, you're not a 1st Century Jew - you're a Modern Day Believer whose head has been filled with the ideas of men.
You read - Luke 16:
16. The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it.
But this time you scratch your head and actually ask - 'Bible - what do
you mean by "were until John?'
"Glad ya asked, son - actually
another passages tells ya.'
Matthew 11:
12. And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force.
13. For all the prophets and the law
prophesied until John.
Here, see if this helps - no need to read into things...
John 1:
43. The day following Jesus would go forth into Galilee, and findeth Philip, and saith unto him, Follow me.
44. Now Philip was of Bethsaida, the city of Andrew and Peter.
45. Philip findeth Nathanael, and saith unto him, We have found him, of whom Moses in the law, and the prophets, did write, Jesus of Nazareth, the son of Joseph.
46. And Nathanael said unto him, Can there any good thing come out of Nazareth? Philip saith unto him, Come and see.
47. Jesus saw Nathanael coming to him, and saith of him, Behold an Israelite indeed, in whom is no guile!
48. Nathanael saith unto him, Whence knowest thou me? Jesus answered and said unto him, Before that Philip called thee, when thou wast under the fig tree, I saw thee.
49. Nathanael answered and saith unto him, Rabbi, thou art the Son of God; thou art
the King of Israel.
Fact is, there is more than one gospel, or good news "in the Bible."
Luke 24:
21. But we trusted that it had been he which should have redeemed Israel: and beside all this, to day is the third day since these things were done.
22. Yea, and certain women also of our company made us astonished, which were early at the sepulchre;
23. And when they found not his body, they came, saying, that they had also seen a vision of angels, which said that he was alive.
24. And certain of them which were with us went to the sepulchre, and found it even so as the women had said: but him they saw not.
25. Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken:
26. Ought not Christ to have suffered these things, and to enter into his glory?
27. And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.
Acts 1:
6. When they therefore were come together, they asked of him, saying, Lord, wilt thou at this time restore again the kingdom to Israel?
7. And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power.
8. But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost
part of the earth.
Obviously, something took place between Mark 1:15 and Acts 1:7, and again, at Acts 7:51 in light of Matthew 12:30-32.
And you can ask what the heck I am talking about, or you can read those passages and end up at Romans 11:25-29 on your own - just you and the Book.
That your questions then be much more informed ones.