When Abraham received the angelic announcement that God would give him the Promised Land, Hebrews , too, requested a confirming sign ( Genesis 15:8), which God provided. However, Zechariah should have simply believed the angel"s announcement and given God thanks for it, as Abraham later did ( Genesis 17:17-18), and as Manoah and his wife did ( Judges 13:2-21). Instead he asked for some verification of the promise, probably a sign (cf. Luke 11:29). The angel gave him a sign, but it cost Zechariah inconvenience and embarrassment for nine months (cf. Luke 1:34; Luke 1:45). Perhaps Zechariah"s request for a sign received a rebuke and Abraham"s did not because Zechariah had the advantage of the Old Testament record, whereas Abraham did not. The angel helped Zechariah understand the seriousness of his mistake by explaining who he was. [source][source][source]
". . . Gabriel was regarded in tradition as inferior to Michael; and, though both were connected with Israel, Gabriel was represented as chiefly the minister of justice, and Michael of mercy; while, thirdly, Gabriel was supposed to stand on the left, and not (as in the Evangelic narrative) on the right, side of the throne of glory." [1][source]
Gabriel (lit. man of God) had appeared twice to Daniel to give him information and understanding ( Daniel 8:16; Daniel 9:21). He did the same for Zechariah here (cf. Luke 1:67-79). Gabriel could have been harder on Zechariah than he was, but he was not probably because Zechariah believed and only wanted confirmation (cf. Judges 6:36-40; Judges 13:2-21). He was not asking for a sign so he could believe. [source][source][source]
The sign that God gave, Zechariah"s dumbness, served to heighten the wonder of what God would reveal and to conceal Gabriel"s revelation from the people until the proper time. [source][source][source]