In the days of the pagan and Jewish leaders, civil and ecclesiastical-came the summons to the son of Zacharias in his solitude in the wilderness.
From childhood, he had been designated for some great work, and he knew it; his whole early life had been a training for it; and at last the summons came.
We are not told of its special form; it was doubtless a theophany, or a vision somewhat similar to the which revealed to Moses and Isaiah, to Jeremiah and Ezekiel.
He had lived a solitary life, and had not learnt his doctrine from men, but had his mission, ministry, and baptism, from heaven.
[Excerpt from the Pulpit Commentary & Gill's Exposition of the Entire Bible]