God provided confirmation to the Holy Spirit's promise.
Joseph and Mary had at least 9 months to get used to the idea of her giving birth to the Christchild.
Yet as those months slowly passed for them, I'm sure they must have wondered within themselves and probably aloud to each other just how it would all be brought to pass.
Afterward, as the emotions of childbirth flooded Mary, she pondered everything in her heart, kept her own counsel; but she must have had a moment or two of wondering if she had remembered, correctly, everything the angel said to her, if her son would truly be great and reign over Israel.
Just a short time later, as they went into the temple to offer up a sacrifice for the birth of their son, God sent Simeon to confirm all that the angel had told Mary and Joseph. Once again, they marvelled at the things told them.
How merciful God is to send us reassurance when we most need it.
Has the Lord given you a promise? Has He whispered some truth into your ear as you read His Word and meditated on His Scriptures.
If so, don't doubt His Word. If He promised it, He will perform it.
And, I have no doubt that He will give further assurances and confirmations of His promise to you, just as He did to Joseph and Mary.
II Corinthians 1:20 "For all the promises of God in him are yea, and in him Amen, unto the glory of God by us."