(Which he had promised afore by his prophets in the holy scriptures,)

The promises of God. When God makes a promise, He keeps it for good. God made quite a promise to Abraham. Thousands of years ago he said
"That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore;

Look at Abraham's seed today. The Christians, the Jews and the Moslems all call him father. To the Christian he is the father of the faithful to the Jew the Father of Judaism, to the Moslem the father of Ishmael. I'm seeing lots of stars and lot's of sand in one great promise among many God has made.

Jesus was walking with two on the way to Emmaus. One was named Cleopas. He told them everything about himself in the scriptures. I wish I heard what he had said. "And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself."

He may have said,
"I'm the lilly of the valley,
the bright and morning star,
the alpha and omega,
the beginning and the end,
wonderful,
counselor,
prince of peace,
the mighty God,
the everlasting Father,
the prince of peace,
the vine,
the branch,
the root of Jesse,
the root of David,
the Lion of the tribe of Judah,
the Bread of Life,
the Temple,
the tabernacle in the wilderness,
the balm of Gilead,
Rehabs red thread,
the origin of Samson's strength,
the Author and finisher of our faith,
the Rock,
the Shepherd,
the Captain of our souls,
the Son of Man,
the Son of God,
the Ancient of Days,
the passover lamb,
the blood on the doorposts,
the Lord of Lords,
the King of Kings,
a priest after the order of Melchisadec,
the Finger of God,
the one on the Throne,
the interpreter of dreams,
the bronze snake Moses held up in the desert,
the ladder Jacob saw when he ran from home,
the Promise of the Father,
the ark of the covenant,
Noah's ark,
the salvation of Israel,
the earnest of our inheritance,
Rebecka's rings of gold,
the Rock in the desert that Moses struck and out flowed water to feed all of the people,
the sacraficial offering,
the Potter in the Potter's house,
the great I AM,
the wisdom of Solomon,
Angel of God who fought with Jacob,
the Holy one of Israel,
the Lover in the Song of Songs,
the God of Job...
and on and on it goes.

There is another very important promise from Jesus Christ.

And, behold, I send the promise of my Father upon you: but tarry ye in the city of Jerusalem, until ye be endued with power from on high.

This is where Jesus mentions the promise of the gift of the Holy Ghost. A truly awesome promise. The promise of a power from on high. God's spirit living inside of you.