A lot of people claim to be Christians, but their works don’t always line up with their words. They may be professors of the faith, but have never been true possessors of the faith. Not everyone who claims faith in Jesus Christ actually knows Him in a personal and saving way. If the Spirit of God has truly come to take up residence in your heart, then the fruit He produces will be evident in your life. New life on the inside will show up on the outside.
The person who has truly come to faith in Jesus Christ is someone who has been made alive in Christ. The life of God that is possessed inwardly will be observable in a person’s life. It shows up through new behaviors that were not present before. That’s what we are able to see here at the close of Acts 2 as these new believers are brought into fellowship, and their faith is expressed outwardly.