This is the house of the Lord God - The double miracle - that of the angelic appearance and that of the fire from heaven - had convinced David that here he had found the destined site of that “house” which it had been told him that his son should build 1 Chronicles 22:10. Hence, this public announcement.
Related Commentaries of 1 Chronicles 22:1
1 Chronicles 22:1
1 Then David said, This is the house of the LORD God, and this is the altar of the burnt offering for Israel.