"Many sincere believers are too introspective. They look too exclusively within, so that their hope is graduated by the degree of evidence of regeneration which they find in their own experience. This, except in rare cases, can never lead to the assurance of hope. We may examine our hearts with all the microscopic care prescribed by President Edwards in his work on The Religious Affections, and never be satisfied that we have eliminated every ground of misgiving and doubt. The grounds of assurance are not so much within, as without us."
Charles Hodge, Systematic Theology (London, 1873), 3:107
HT: Tony Reinke