Sincere is not enough
From this plain account of the threefold state of man, the natural, the legal, and the evangelical, it appears that it is not sufficient to divide mankind into sincere and insincere. A man may be sincere in any of these states, not only when he has the Spirit of adoption, but while he has the spirit of bondage to fear. Yes, while he has neither this fear, nor love. For undoubtedly there may be sincere heathens, as well as sincere Jews or Christians. This circumstance, then, does by no means prove that a man is in a state of acceptance with God.
1771 text
IV. 1. From this plain account of the three-fold state of man, the natural, the legal, and the evangelical, it appears, that it is not sufficient, to divide mankind, into sincere, and insincere. A man may be sincere in any of these states; not only when he has the Spirit of adoption, but while he has the spirit of bondage unto fear. Yea, while he has neither this fear, nor love. For undoubtedly there may be sincere Heathens, as well as sincere Jews or Christians. This circumstance then, does by no means prove, that a man is in a state of acceptance with God.