A harp or a lyre? Both harps and lyres were hand-held stringed instruments with wooden frames.
Summers in Israel can be very hot, depending on where one is (see 32:4). In places like Masada, near the Dead Sea, temperatures can soar past 110 degrees Fahrenheit (43° C) without a drop of rain. However, Jerusalem, with its higher elevation, remains cooler with temperatures between 75 and 85 degrees (24 to 29° C).
The term house of the Lord (27:4) always refers to the temple, where God in OT times lived among his people.
What does Selah mean? Although the word Selah is found 39 times in the book of Psalms, its exact meaning is uncertain. Most scholars believe it is a musical term or a term to be used by a worship leader, possibly to mark a pause.