"20And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation: 21Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you." (Luke 17: 20-21)
Rightly dividing the Word of Truth (2 Timothy 2: 15), we can better understand passages like this one.
How is that the Pharisees would have the Kingdom within them, when many of then had rejected Jesus as the Messiah (Matthew 12)
Jesus was still ministering on earth as the perfect Man, who had not yet died for our sins, who had not yet been raised for our justification (Romans 4: 25).
The point that Jesus was making is that the Kingdom is not some place that we search for.
The Kingdom of Heaven came to us:
"From that time Jesus began to preach, and to say, Repent: for the kingdom of heaven is at hand." (Matthew 4: 17)
Now, what is the Kingdom of Heaven, or the Kingdom of God, for those terms are interchangeable:
"For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost." (Romans 14: 17)
Righteousness is a gift, in which we are established because of Jesus:
"For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him." (2 Corinthians 5: 21)
Because we have been justified by faith, we have peace with God (Romans 5: 1)
With this peace, we have the fruit of His Spirit breaking forth in us: love, joy, peace (Galatians 5: 22-23)
The Kingdom of Heaven is the Holy Spirit living in us, and we have His Spirit because of Jesus:
"33Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear." (Acts 2: 33)
Today, you and I are not looking for the Kingdom of Heaven, but in fact we have received this Kingdom because we believe in Jesus, and have received Himself into us.