They did not yet understand the Scripture, that He must rise again from the dead.
John 20:9
But these are written, that ye might believe that Jesus is the Christ,
the Son of God; and that believing ye might have life through His name.
John 20:31
The Lord Himself shall give you a sign. Behold, a virgin shall conceive,
and bear a son, and shall call His name Immanuel.
Isaiah 7:14
And the glory of the Yehowah shall be revealed,
and all flesh shall see it together: for the mouth of the Yehowah hath spoken it.
Isaiah 40:5
Jesus, who is Jehovah become flesh, is called the Son of God. Therefore,
the name Jesus Christ means “Jehovah is salvation.”
John prepared the way of Yehowah, not the way of a second person of a triune God.
The God of all the prophets was not a Trinity, but Jehovah God alone.
The God of all the apostles was also Jehovah God who became flesh as Jesus Christ.
For them, Jehovah was the one and only God, and Jesus was the one and only God revealed in the flesh.
Believing that God is the Father and, at the same time,
the Son is completely different from believing
that the Father and the Son are different persons who are nevertheless one God.
The Gospel ordained by God is concerning His Son,
whom the prophets wrote about. When that God became flesh,
He came through the lineage of David.
This is the Gospel:
The God who promised to abolish death Himself came to this earth in the form of a man,
died on the cross, and rose again from the dead. Hallelujah!