Later in the book of  Luke it is recorded that Zacharias and Elizabeth's son John is in his mother's womb. God's plan for John is to for him to prepare the way of the Lord.
Luke 1:41-44
And it happened, when Elizabeth heard the greeting of Mary, that the babe leaped in her womb; and Elizabeth was filled with the Holy Spirit.  Then she spoke out with a loud voice and said, “Blessed are you among women, and blessed is the fruit of your womb!   But why is this granted to me, that the mother of my Lord should come to me?   For indeed, as soon as the voice of your greeting sounded in my ears, the babe leaped in my womb for joy.
Notice, the babe leaped for joy. As you are preparing your heart, are you "leaping for joy" in expectation of Christ's coming?