Jn 2:22, Jn 12:16, Rom 1:4, Jn 3:14
No one believed in Jesus as the Christ until Jesus was crucified and resurrected. (Jn 8:28)
Jn 8:28 Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am he, and that I do nothing of myself; but as my Father hath taught me, I speak these things.
In the Old Testament it was foretold that Christ would die on the cross. God nailed Christ to the cross to save us. Those who believe in Jesus as the Christ have eternal life. (Jn 3:14-16)
Jn 3:14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: 15 That whosoever believeth in him should not perish, but have eternal life. 16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
The Holy Spirit raised Jesus from the cross on the third day. (Rom 1:4)
Rom 1:4 And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
After Jesus died on the cross and rose from the dead on the third day, the disciples truly believe that Jesus is the Christ. (Jn 2:22, Jn 12:16)
Jn 2:22 When therefore he was risen from the dead, his disciples remembered that he had said this unto them; and they believed the scripture, and the word which Jesus had said.
Jn 12:16 These things understood not his disciples at the first: but when Jesus was glorified, then remembered they that these things were written of him, and that they had done these things unto him.