There are few higher compliments one can give another human being than to say, "I know I can rely on your word. You speak the truth and what you say you will do, you do." Kept promises, it has been said, are the glue that hold the universe together.
What if person I am speaking to is a Person, the divine Person, God himself? That is the heart of the Christian religion. What God has promised he will fulfill. Such is the message of Christmas and Easter.
As Zechariah sang at the birth of his son, John the Baptizer,
Praise be to the Lord, the God of Israel, because he has come to his people and redeemed them. He has raised up a horn of salvation for us in the house of his servant David
(as he said through his holy prophets of long ago), salvation from our enemies and from the hand of all who hate us---to show mercy to our ancestors and to remember his holy covenant,
the oath he swore to our father Abraham: to rescue us from the hand of our enemies, and to enable us to serve him without fear in holiness and righteousness before him all our days.
And you, my child, will be called a prophet of the Most High; for you will go on before the Lord to prepare the way for him, to give his people the knowledge of salvation through the forgiveness of their sins, because of the tender mercy of our God,
by which the rising sun will come to us from heaven to shine on those living in darkness and in the shadow of death, to guide our feet into the path of peace.
Luke 1:67-80