The trumpet (that is, a ram’s horn) served multiple purposes in Israel’s history, not the least of which was to summon the people to battle (Judges 3:27; Judges 6:34; 1 Samuel 13:3), that being also the case here (Nehemiah 4:20). That the trumpet-sounder stayed at Nehemiah’s side implied that Nehemiah himself remained present somewhere along the wall, undoubtedly to survey progress, encourage the labourers, and stay in touch with the leaders
who kept a watchful eye on potential threats. As Nehemiah heard of threats from the leaders, he would give the command to the blower to sound his trumpet. This use of the trumpet again recalls Israel’s history, specifically that the battle is ultimately the Lord’s, to be fought in faith (Nehemiah 4:20b).
18 And each of the builders had his sword strapped at his side while he built. The man who sounded the trumpet was beside me.