Although it is the father of John the Baptist who is speaking, his initial focus, not on his own child, but on the child of Mary, emphasises that it is Christ who has the pre-eminence. John takes his rightful place behind the one who will come after him, but was before him.
We worship God for his interventions. He is the God who acts in history, and in very definite ways. The promises of the Old Testament need to be fulfilled, and this prophecy speaks to how Christ will come and his coming will be reported and publicised by reliable witnesses, and so that it can be examined and studied. The Christian faith is not a matter of vague and indistinct prophecies which can be easily disputed. It is a matter of clear and detailed events which God does not fail to bring about. We worship God because he does not forget a single word that comes out of his mouth. His children hang on his every word, and when those words were uttered long ago, and do not seem likely to have a fulfilment, they may be tempted to despair. But great is their thankfulness when after many years, God proves that he has forgotten nothing he has said, and they were right not to give up looking a clear fulfilment.