There are over-simplifications given to describe a child of God. Three aspects are to be called and chosen and faithful in following Jesus Christ. Called to stop sinning and learn to do right is first and that means belief in what Chist says: "Stop sinning". Those believing it find they are given the Holy Spirit and miracles by God Himself. The calling is to many but the grace of receiving the calling is given to far fewer people. Having received the calling to be a saint with Holy Spirit leadership it is vital to continue to the end of life, holding fast to the calling and teachings of Christ and truth of the Spirit and if we do we know we are really what God describes as children of His. Of course other aspects of real faith are rewarded or recognised by God by His giving miracles and the Holy Spirit: Simply believing that He is the Creator is a starting point of faith. Believing that Christ died for you is another instance of faith that God rewards. Still the faithfulness is required to continue such a progress into faith through all of life. That is being called and chosen and faithful. And letting it lead how you live. The example we are given is Abraham and in Galatians Paul taught that such as these who live by faith are children of Abraham. I also find a good description of living by faith is John Bunyan's "A Pilgrim's Progress" allegory and the hymn of his "Who would true valour see" or "To be a pilgrim". This is an individual Christian but the body of local believers which is a church or assembly (or some other term depending on culture) is something again when the individuals believe themselves to be joined spiritually in Christ. Yet it does not substitute the need for the individuals to walk the eternal life of faith as children of Abraham and become transformed and sanctified as children of God. When travelling with a coach party in foreign countries each individual still needs their own passport. Finding you were mistakenly relying on the group for your passport is a nightmare scenario, like the man in the parable who finds himself at a banquet in the wrong clothes.
