How do we know John is talking about true believers as sons of God?

In the context of 1 John 3:1, John emphasizes a particular group who are called the sons of God – those chosen and loved by the Father. This is further clarified since not everyone is inherently a child of God; rather, it is through faith in Christ that we become children of God (John 1:12). John distinguishes between those who are recipients of God's grace and love versus those who may claim the title without the genuine relationship with Christ. Thus, true sonship is based on one’s belief and trust in the redemptive work of Jesus.