People of Israel were God's kingdom in the past

A selection of verses showing this theme:

The people of Israel were selected by God at Sinai to be God’s kingdom:

Exodus 19 verses 5 - 6

5 Now therefore, if you will indeed obey my voice, and keep my covenant, then you shall be my own possession from amongst all peoples; for all the earth is mine; 6 and you shall be to me a kingdom of priests, and a holy nation.’ These are the words which you shall speak to the children of Israel.”

This was not because of special merit of theirs but because of God’s promises to their ancestors Abraham, Isaac and Jacob. It placed them in a position of responsibility to keep God’s commandments

Deuteronomy 7 verses 6 - 8

6 For you are a holy people to the LORD your God. The LORD your God has chosen you to be a people for his own possession, above all peoples who are on the face of the earth. 7 The LORD didn’t set his love on you nor choose you, because you were more in number than any people; for you were the fewest of all peoples; 8 but because the LORD loves you, and because he desires to keep the oath which he swore to your fathers, the LORD has brought you out with a mighty hand and redeemed you out of the house of bondage, from the hand of Pharaoh king of Egypt.

When the Israelites wanted a king like the surrounding nations. Samuel their judge at that time felt rejected. God points out that it was His kingship that was being rejected:

1 Samuel 8 verses 5 - 7

5 They said to him, “Behold, you are old, and your sons don’t walk in your ways. Now make us a king to judge us like all the nations.” 6 But the thing displeased Samuel when they said, “Give us a king to judge us.” 
Samuel prayed to the LORD. 7 The LORD said to Samuel, “Listen to the voice of the people in all that they tell you; for they have not rejected you, but they have rejected me as the king over them.

Since God was their king the kings of Israel ruled on his behalf and their throne was considered to be God’s throne. David makes this clear at the appointment of Solomon as his successor:

1 Chronicles 28 verse 5

5 Of all my sons (for the LORD has given me many sons), he has chosen Solomon my son to sit on the throne of the LORD’s kingdom over Israel.

However Jesus warned his contemporaries that their special position as the kingdom of God would cease because of their rejection of him as their Messiah. That privilege would be given to those who would become Jesus’ disciples:

Matthew 21 verse 43

43 “Therefore I tell you, God’s Kingdom will be taken away from you, and will be given to a nation producing its fruit.