John Trapp on Zechariah 3:6

Verſe 6. And the Angel of the Lord proteſted] Either with an oath or ſome deep aſſeveration, or both; as 1 Sam. 25.26. As the Lord liveth, and as thy ſoul liveth &c. The former is an oath, the latter an aſſeveration or obteſtation only, conjoyned with that oath. Among the Heathens Ex animi ſeu ſententia was inſtead of an oath: And rather then ſwear or ſay more, in a matter of no great moment, Chinius the Pythagorean would undergoe a mulct of three talents. Others render it Teſtified, or called witneſſe upon his words, the Angels and the prophet there preſent, for the more aſſurance. Thus, though Chriſts word be ſufficient (for he is Amen, the faithful and true witneſſe) yet for his ſervants better ſettlement,Rev. 3.14. he hath bound his promiſes to them with an oath, and taken heaven and earth to witneſſe; which is dignatio ſtupenda, a wonderful Condeſcenſion.