To confess the Lord Jesus and to truly believe in Him is not possible to do with a heart of a natural, unsaved, man. To be able to do so comesRomans 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.
10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
only as a byproduct of salvation, not before.
The heart of an unsaved natural man:
[Jer 17:9 KJV] 9 The heart [is] deceitful above all [things], and desperately wicked: who can know it?
The heart of the saved:
[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.
[2Co 3:3 KJV] 3 [Forasmuch as ye are] manifestly declared to be the epistle of Christ ministered by us, written not with ink, but with the Spirit of the living God; not in tables of stone, but in fleshy tables of the heart.