(Act 7:47) But Solomon built him an house.
(Act 7:48) Howbeit the most High dwelleth not in temples made with hands; as saith the prophet,
(Act 7:49) Heaven is my throne, and earth is my footstool: what house will ye build me? saith the Lord: or what is the place of my rest?
(Act 7:50) Hath not my hand made all these things?
(1Ki 8:27) But will God indeed dwell on the earth? behold, the heaven and heaven of heavens cannot contain thee; how much less this house that I have builded?
We read that "Heaven is my throne". Apparently, the heaven of heavens is meant, that is, the highest heaven is the throne of God. Clearly, the highest heaven cannot be above God, for God is the Most High (Ac 7:48). Moreover, no heaven can contain God (1Ki 8:27). Thus, since the highest heaven is above all other heavens and God is not contained by it, the highest heaven can be associated with the throne of God. Now, since the earth is the footstool of God, we could conclude that earth is at the lowest place. The heavens that we see with our eyes could be associated with the firmament of the vision of Ezekiel. In the vision, the firmament was below the throne (Ez 1:26). While in the vision of Ezekiel the view was from below the firmament, in Rev 4 the view is from above. In Rev 4 we read of a sea of glass. The sea is compared to crystal, just like the firmament in Ez 1:22. We could reason that they are the same.
(Rev 4:6) And before the throne there was a sea of glass like unto crystal ...
The footstool of the Lord was mentioned also by David in this passage.
(1Ch 28:2) Then David the king stood up upon his feet, and said, Hear me, my brethren, and my people: As for me, I had in mine heart to build an house of rest for the ark of the covenant of the LORD, and for the footstool of our God, and had made ready for the building:
(Psa 99:1) The LORD reigneth; let the people tremble: he sitteth between the cherubims; let the earth be moved.
(Psa 99:5) Exalt ye the LORD our God, and worship at his footstool; for he is holy.
The Lord Jesus mentioned the throne of God and the footstool of God in the following passage.
(Mat 5:34) But I say unto you, Swear not at all; neither by heaven; for it is God's throne:
(Mat 5:35) Nor by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King.
(Psa 113:4) The LORD is high above all nations, and his glory above the heavens.
(Psa 113:5) Who is like unto the LORD our God, who dwelleth on high,
(Psa 113:6) Who humbleth himself to behold the things that are in heaven, and in the earth!