This evening, I determined to learn more about some aspect that I had overlooked for many years. And thinking would be great to look at it from the Gospel. So decided to use Luke, as his gentile audience.
Then, it started 
"...and he will go before him in the spirit and power of Elijah,..." ~ Luk 1:16 ~
Who is "he" that will go before? He is John (v.13)
Who is "him" that John will go before? Him refers to the Lord, God of Israel (v.14)
What does it mean for John to go before the Lord in the spirit and power of Elijah? John will turn the hearts of people. The turning hearts are important as preparing people for the Lord ("to make ready for the Lord a people prepared" v.17).
Why is it important? Simple. Because God will visit the people soon, but the people are not prepared. When the Lord visits His people, He want them to meet him prepared. He wants ready people. And in those days, the people are not yet ready. Their hearts need to be turned. And that's John's mission was. To turn people's heart.
But, isn't it the job of God to turn people's heart? No human being could change heart except God's alone? Exactly!! That's why in v.15 before that, the angel announced that John would be filled with the Holy Spirit, even from his mother's womb. It's the work of the Holy Spirit to turn people's heart. And He works through people; like John, whom is filled. May i say then, John went in the spirit and power of Elijah as a metaphor as John is filled with the Holy Spirit to turn people's heart, preparing a people ready for the Lord.
Ok, so what? If John was filled with the Holy Spirit to accomplish that task, what has it to do with us? I think many!! We want to see people changed. We know it's only by the work of the Holy Spirit. However, Holy Spirit uses people to do the work. Man and woman, whom filled with the Holy Spirit, such that they go with the spirit and power of Elijah.
So, where could we find such people? I think the time still open. John was the first person (as far as i know). And later, in Acts 2, in the day of Pentacost, the Holy Spirit filled the 120 and they did mighty work to began the early church. Peter quoted Joel to explain that day as the last day that Joel spoke:
"And in the last days it shall be, God declares, that I will pour out my Spirit on all flesh, and your sons and your daughters shall prophesy,
and your young men shall see visions,
and your old men shall dream dreams;
even on my male servants and female servants
in those days I will pour out my Spirit, and they shall prophesy."
~Acts 2:17-18~
I believe the day has not finished. That God pouring His Holy Spirit, to accomplish His work; turning people's heart. His work is through human hands and feet, and mouth, and eyes, and the whole person's life.
So I would like to close with the last application below:
Then, what's the role of Zechariah & Elizabeth in the story? I think they have significant roles there, as Luke recorded in v.8, both of them were righteous before God (a term so powerful unfortunately would discuss this another time)
"And they were both righteous before God, walking blamelessly in all the commandments and statutes of the Lord." ~v.8~
For again later Luke recorded that the angel reassured Zechariah of his righteous life and God's favor upon his family.
"But the angel said to him, "Do not be afraid, Zechariah, for your prayer has been heard,...". ~v.13 ~
As James would support the fact Zechariah's prayer was heard, because he is a righteous person, and he lives a righteous life:
"The prayer of a righteous person has great power as it is working" ~Jam 5:16~
It started with this righteous couple who upholds God's decree and live it. And they prayed to God. And God answered their prayers. Amen to that. And I believe, He is God who hears and answers prayers. So the prayers for the Holy Spirit to fill us, that we will go with the spirit and power of Elijah, to make ready people prepared for the Lord!
For it's the day of salvation. The year of the Lord's favor. While there's still time, before the Lord's return again, let's brave ourselves. "Visit us again Lord, and like we were told, the works of your hands in days of our fathers, we long to see it again, in our days Lord."
O God, we have heard with our ears,
our fathers have told us,
what deeds you performed in their days,
in the days of old: ~Ps 44~