Seeking and finding. Finding what? Continuing with the message Jesus gave during the Sermon on the Mount, He told the Jewish people under the law to seek and they would find. Knock and it would be opened to them. Seek what? Prior to this He said to seek first the kingdom (Jesus Himself) and His righteousness. This was new to them. This would take away their right to judge others as they did under the law. They will find the right-standing with God they seek and the narrow gate of His righteousness would be opened to them when they knocked.
During the sermon on the mount, Jesus told His Jewish audience who were under the old covenant law to seek first the kingdom of God and His righteousness... This was a switch from the system they had been under where they sought to establish their own righteousness (or right-standing with God). The good news gospel has revealed something that had been previously concealed and that is God's righteousness given to us as a gift. As new covenant believers, this is something we no longer need to seek. It now identifies us. When it comes to His righteousness, look no further than where you are right now. He lives in you.