Although hypocrites and other unregenerate men may vainly deceive themselves with false hopes and carnal presumptions of being in the favor of God, and estate of salvation (which hope of theirs shall perish): yet such as truly believe in the Lord Jesus, and love him in sincerity, endeavoring to walk in all good conscience before him, may, in this life, be certainly assured that they are in the state of grace, and may rejoice in the hope of the glory of God, which hope shall never make them ashamed. (Westminster Confession of Faith 18:1)
This section teaches that unregenerate people may possess a false sense of assurance but that genuine believers may attain a true sense of assurance. Assurance must be considered for the four kinds of people in the world.
The first group of people are not saved and are aware that they are not. They are unregenerate and they know it. They have no interest in becoming Christians.
The people in the second group are in a state of grace, but they are not sure that they are saved. The confession, as we will see, says that assurance of salvation is possible and indeed should be sought. Nevertheless, not everyone who is in the state of grace has yet arrived at the conclusion that he is in that state. Such people may think or hope they are saved but may not have full assurance that they are. Their degree of assurance vacillates from firm to shaky. During our study of the perseverance of the saints, we indicated that they can fall seriously and radically, but not fully and finally. When people are in the midst of a serious fall, they can have grave questions about the state of their soul.