What is “the kingdom” and what are “all these things” in Matthew 6:33?

The words are taken from Matthew 6:31-33, where Jesus says

Do not be anxious, saying ‘What shall we eat?’ or ’What shall we drink?’ or ‘What shall we wear?’ For the Gentiles seek after all these things, and your heavenly Father knows that you need them all. But seek first the kingdom of God and his righteousness, and all these things will be added to you.

The Bible promises (Revelation 11:15) that there will come a time when “The kingdom of the world has become the kingdom of our Lord and of his Christ, and he shall reign forever and ever.” Jesus Christ will return to the earth, he will raise the dead, the faithful will be rewarded with eternal life, and a righteous government will be set up over the whole world. We pray for this wonderful time with the words, “Thy Kingdom come, Thy will be done on earth as it is in heaven.”

Jesus is saying in Matthew 6 that we should not worry about the cares of our daily lives, but that our efforts should be directed towards developing characters that are suitable for the Kingdom that is to come.