How long wilt thou be angry? — Literally, until when hast thou fumed? A pregnant construction combining two clauses. Thou hast been long angry; how long wilt thou continue to be angry? (Comp. Psalms 13:2, Note, and Exodus 10:3.) Others say the preterite here has the sense of a future perfect, which comes to the same thing: “How long wilt thou have fumed? (See Müller’s Syntax, § i. 3, rem. (a), Prof. Robertson’s trans.)
Against the prayer. — Literally, in, i.e., during the prayer. The smoke of the Divine anger is, perhaps, conceived of as a cloud through which the prayer (often symbolised by an ascending incense) cannot penetrate.