Choose to] believe upon the Lord Jesus Christ and you will be immediately saved when you believe.
The question you should have asked is who will believe and why will they believe? Man cannot give belief to himself - it is given only by God, as a byproduct of salvation. Therefore, until being given a new heart (from salvation), the spiritually dead will never/ can never "choose to believe"
[Phl 1:29 KJV] 29
For unto you it is given in the behalf of Christ, not only to believe on him, but also to suffer for his sake;
[
Jhn 10:26 KJV] 26
But ye believe not, because ye are not of my sheep, as I said unto you.
[
Jhn 5:38 KJV] 38 And
ye have not his word abiding in you: for whom he hath sent, him ye believe not.
[
2Co 4:3-5 KJV]
3 But if our gospel be hid, it is hid to them that are lost:
4
In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
5 For we preach not ourselves, but Christ Jesus the Lord; and ourselves your servants for Jesus' sake.
[
Gal 2:16 KJV] 16 Knowing that a man is not justified by the works of the law, but
by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
[Jhn 12:37-40 KJV]
37 But though he had
done so many miracles before them, yet they believed not on him:
38 That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed?
39
Therefore they could not believe, because that Esaias said again,
40
He hath blinded their eyes, and hardened their heart; that they should not see with [their] eyes,
nor understand with [their] heart, and be converted, and I should heal them.
[Jer 17:9 KJV] 9
The heart [is] deceitful above all [things], and desperately wicked: who can know it?
[Eze 36:26 KJV] 26
A new heart also will I give you, and a new spirit will I put within you: and I will take away the stony heart out of your flesh, and I will give you an heart of flesh.
[Rom 10:10 KJV] 10
For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
[2Pe 1:3 KJV] 3 According as
his divine power hath given unto us all things that [pertain] unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
[1Co 2:14 KJV] 14
But the natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know [them], because they are spiritually discerned.