Praise be to the God and Father of our Lord Jesus Christ! In his great mercy he has given us new birth into a living hope through the resurrection of Jesus Christ from the dead, and into an inheritance that can never perish, spoil or fade—kept in heaven for you (1 Pet 1:3-4), …

“An inheritance that can never perish, spoil or fade” is what we inherit as heirs of God, which is, indeed, different from what people usually seek in this world—food, clothes, and other things that perish, spoil and fade. Jesus said:

For the pagans run after all these things, and your heavenly Father knows that you need them. But seek first his kingdom and his righteousness, and all these things will be given to you as well (Matt 6:32-33).

“All these things” are what pagans seek, but we as children of God know that our Father knows we need them and makes certain that we have them. And if we know that all these things are given to us, the only things we should seek now are “his kingdom and his righteousness.” The parallel passage in Luke says:

But seek his kingdom, and these things will be given to you as well. Do not be afraid, little flock, for your Father has been pleased to give you the kingdom (Luke 12:31-32).

If we can see that our Father is pleased to give us what we need, we can surely see that he is even more pleased to give us his kingdom. In fact, God’s kingdom is the inheritance he gives to his children, and is something that is the most valuable of all we can seek. That is why Jesus told us to seek it “first”—more than anything.

Note that God’s kingdom is mentioned also in the Lord’s Prayer:

When you pray, say: "Father, hallowed be your name, your kingdom come (Luke 11:2). …

It is important to know that this kingdom is not the heaven that Christians will enter after they leave this world. Note that Jesus told his disciples to pray, “your kingdom come.” That means that they were to pray that it would “come” to where they were—the earth. Matthew in his version of the Lord’s Prayer says:

This, then, is how you should pray: "Our Father in heaven, hallowed be your name, your kingdom come, your will be done on earth as it is in heaven (Matt 6:9-10). …

God’s kingdom is the place where his will is done. Therefore, to pray that his will be done on earth is the same as to pray that his kingdom come to the earth.

In Luke 11, Jesus’ teaching on the Lord’s Prayer is followed by the parable of the one who asks his friend to give three loaves of bread, and that of a son asking his father to give a fish or an egg. These stories including the teaching on the Lord’s Prayer should be treated as one passage under the motif of prayer, and Jesus’ conclusion is:

If you then, though you are evil, know how to give good gifts to your children, how much more will your Father in heaven give the Holy Spirit to those who ask him (Luke 11:13)!

Note that the passage starts with a command to pray for God’s kingdom to come, and ends with the promise of the Father to give the Holy Spirit.