Its a work of God !
To believe on Christ, even though a person does it, for God does not believe for man, but its a work of God Jn 6:29
29 Jesus answered and said unto them,
This is the work of God,
that ye believe on him whom he hath sent.
It is God's business, Employment that ye believe on Christ His Son, whom He hath sent !
There are certain ones God sent His Son to save, like Matt 15:24
24 But he answered and said,
I am not sent but unto the lost sheep of the house of Israel.
Now primarily its the Work of God the Holy Spirit, when He comes to one of the Sheep of the Lost Sheep of Israel, whether jew or Gentile [Jn 10:16] with the Gospel, causing it to be unto them the Power of God, which causes them to believe Rom 1:16
16 For I am not ashamed of the gospel of Christ: for
it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek.
That word power here is the same greek word here attributing believing to the Power of the Holy Ghost Rom 15:13
Now the God of hope fill you with all joy and peace in
believing, that ye may abound in hope,
through the power G1411 of the Holy Ghost.
The word is the greek word dynamis and means:
I.strength power, ability
A.
inherent power, power residing in a thing by virtue of its nature, or which a person or thing exerts and puts forth
B.
power for performing miracles
C.
moral power and excellence of soul
D.
the power and influence which belong to riches and wealth
E.
power and resources arising from numbers
F.
power consisting in or resting upon armies, forces, hosts
Gill writes:
"through the power of the Holy Ghost"; not by might or power of man, but by that same divine power which first began the good work, and must fulfil it; which at first implanted the grace of hope, and must perform the work of that, as of faith. The same power is requisite to cause grace to abound, or saints to abound in the exercise of it, as was to the first production of it.
Paul indicates that believers did believe by the working of His Great Power Eph 1:19-20
19 And what is the exceeding greatness of his power
to us-ward who believe, according to the working of his mighty power,
20 Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places,
Now the way to know whether or not the Spirit energized the Gospel with Power, its when the one is caused to believe Rom 1:16, believing is the result of the Gospel being energized by the Spirit ! It gives it positive effectiveness and application, resulting in their believing !
But wonder if one does not believe the Gospel, or believe on Christ ? That means merely they were not of His Sheep Jn 10:26
26 But
ye believe not, because ye are not of my sheep, as I said unto you.
They are not even suppose to believe because they are not His Sheep and therfore He did not come to save them Matt 15:24 !
So we are impelled to believe that when Jesus made the statement in Jn 6:29, it can only mean to His Sheep, for it was many that it was not God's will to believe, but had been appointed to disobedience 1 Pet 2:8
8 And a stone of stumbling, and a rock of offence, even to them which
stumble at the word,
being disobedient: whereunto also they were appointed.
In fact they were made to stumble at the word by the decree and purpose of God ! That too was the work or doing of God Matt 21:42
42 Jesus saith unto them, Did ye never read in the scriptures, The stone which the builders rejected, the same is become the head of the corner:
this is the Lord's doing, and it is marvellous in our eyes? 9