Jamieson, Fausset and Brown on Zechariah 1:10

10. answered--The "angel of the covenant" here gives the reply instead of the interpreting angel, to imply that all communications through the interpreting angel come from Him as their source.

Lord hath sent to walk to and fro through the earth--If "Satan walks to and fro in the earth" (implying restless activity) on errands of mischief to God's people (Job 1:7), the Lord sends other angels to "walk to and fro" with unceasing activity everywhere to counterwork Satan's designs, and to defend His people (Psa 34:7; 91:11; 103:20, 21; He 1:14).