Adoption in theology is when God chooses to make a person a part of his family through faith in Jesus Christ. This is kind of like how parents choose to make a child a part of their family through adoption. When someone accepts Jesus as their Savior, God adopts them into his family and gives them all the rights and privileges of a child of God. This means that they are forgiven of their sins, have access to God through prayer, and are promised eternal life in heaven. It's like joining a really big and loving family where God is the father and all of the other believers are brothers and sisters.