“my holy mountain...my house of prayer.” When God says “my holy mountain” and “my house of prayer,” He is referring to Mount Zion where the New Jerusalem ruled by Christ will be (cp. Isa. 27:13; 57:13; 65:11), and the new Temple that will be built for the Millennial Kingdom (cp. Ezek. 40-43).
[For more on the Millennial Kingdom, see Appendix 3, Christ’s Future Kingdom on Earth.”]