Baptized in Water and Spirit to enter Kingdom of God VS UN baptized belief in Jesus as seen with the sinner at Calvary?

Just hoping to get your opinion on this, I've been researching the various baptisms and salvation doctrines of Christianity until I came across this seeming contradiction among the qualifications of entering into the Kingdom of Heaven as seen below.

1) Belief in Jesus AND Water and Holy Spirit Baptisms must be obtained.

Mark 16:16
He that believeth and is baptized shall be saved; but he that believeth not shall be damned.

John 3:5
Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and [of] the Spirit, he cannot enter into the kingdom of God.


But the opposing factor below is that NO water was necessary for the sinner on the cross next to Jesus to enter into the Kingdom of God. Which leaves me a bit confuzzled

2) Unbaptized belief in Jesus is sufficient.

Luke 23:39-42
39And one of the malefactors which were hanged railed on him, saying, If thou be Christ, save thyself and us. 40But the other answering rebuked him, saying, Dost not thou fear God, seeing thou art in the same condemnation? 41And we indeed justly; for we receive the due reward of our deeds: but this man hath done nothing amiss. 42And he said unto Jesus, Lord, remember me when thou comest into thy kingdom. 43And Jesus said unto him, Verily I say unto thee, To day shalt thou be with me in paradise.

To further backup this 2nd qualification doctrine, here are some good Scripture that verifies the sinner's salvation based solely upon his belief in Jesus as Lord alone, with no water baptism mentioned at all.

Romans 10:9
That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.

Acts 16:31
And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house.

So why are there 2 different doctrines for qualification into the Kingdom of God? The 1st requiring belief in Jesus and the water baptism and the 2nd only a confessing belief in Jesus Christ as Lord?

I'd love to hear any related Scripture on the matter or humanly perspectives if you feel you are led by the Holy Spirit, thanks and many blessings!

Proverbs 25:2
[It is] the glory of God to conceal a thing: but the honour of kings [is] to search out a matter.