Charles Finney could share no tangible proof of the spiritual experience that transformed him from an attorney into a Christian evangelist. Though the Christian's inward personal assurance of spiritual reality defies complete logical analysis and lacks external and tangible vindication, the believer requires no additional proof because he knows that he knows. Indeed, millions have professed that this inward and very personal assurance has produced peace and joy in living, strength and assistance in sorrow, guidance in decisions, certainty of hope in sickness and death. No other assurance has borne such precious fruit. No other personal conviction has clothed daily living with service to others nor inescapable dying with visions of eternal glory.
Christians testify that personal inward assurance confers satisfying spiritual blessings.
A second strength grows out of the unique power of the Christian's testimony of inward assurance to persuade some unbelievers to seek and receive their own faith relationship. Shared personal assurance becomes contagious. The book of Acts records six opportunities for Paul to speak before unbelievers. In each case the learned Apostle chose to share his personal inward experience rather than to attempt tangible or academic proof for his new faith. Paul relied upon the unique power of the shared testimony of inward assurance to convince and to persuade others.