ANSWER: He had various ways of speaking: (1) through words vibrating in the air like the human voice, only much louder (Ex. 20:22; Deut. 4:33; 5:22-27; Neh. 9:13). (2) By the urim and thummin, as in Num. 27:21; I Sam. 28:6. (3) By the Holy Spirit in the heart convicting the sinner (John 16:8-11), and assuring the believer (Gal. 4:6). The prophets got their messages probably in this way. (4) By writing (Ez. 32:16; Dan. 5:5).
— Steele's Answers p. 266.