He was troubled
Terrifying effect of supernatural appearances
Such has usually been the effect of supernatural appearances, even on good men, as is exemplified in Manoah, David, Paul, and others.
1. Man’s weakness is incapable of easily bearing the glory of such appearances.
2. His sinfulness naturally makes him afraid that the heavenly messenger may be sent to him in displeasure. Hence appear the wisdom and goodness of God in employing, as the heralds of gospel salvation, not angels but human beings, whose terror does not make us afraid. If, however, we shall be so wise for ourselves as to receive the gospel, and to take the Lord of angels for our Lord, then we shall be prepared without fear to meet, not one angel, or a few angels, but the whole angelic host, with the Lord at their head--that host from which the ungodly will shrink in dismay, but which the ransomed shall gladly join round about the throne, to the number of ten thousand times ten thousand, and thousands of thousands. (James Foote, M. A.)
Angelic glory awakening fear
It was partly the suddenness, partly the unexpectedness, and partly the glory of the apparition, that affrighted this good man. Glorious and sudden apparitions do affright even the holiest and best of men. We cannot bear the sight and presence of an angel without consternation and fear, in our frail and sinful state. O happy hour when, mortality and sin being taken out of our natures, we shall not only behold the glorified angels without fear, but the glorious God with delight and love I Lord! let me now see Thee by faith, hereafter by sight. (W. Burkitt, M. A.)
Sight rather than faith the cause of fear
He that had wont to live and serve in the presence of the Master, was now astonished at the presence of the servant; so much difference is there betwixt our faith and our senses that the apprehension of the God of spirits by faith goes down sweetly with us, whereas the sensible apprehension of an angel dismays us. Holy Zachary, that had wont to live by faith, thought he should die, when his sense began to be set on work; it was the weakness of him, that served the altar without horror, to be daunted with the face of his fellow-servant. In vain do we look for such ministers of God as are without infirmities when just Zachary was troubled in his devotions with that wherewith he should have been comforted: it was partly the suddenness and partly the glory of the apparition that affrighted him. (Bishop Hall.)