Testimony
It is plain, from a spiritual understanding of Holy Scripture, that God has ordained the testimony of His saints as the primary vehicle through which He chooses to call lost souls out from death and into eternal life. Testimony, in scripture, is not some practiced recitation of a clever simile, or factual presentation of the Gospel, but a sincere life lived out in thought, word, and deed; a fully integrated expression that speaks and acts according to firmly held belief. The consistent testimony of a growing Christian is an unassailable weapon in God's war on death and lies. A moral person living and responding to the world in Christian patience, charity, peace, and a solid hope of a glorious eternity, even while suffering, or being the subject of strong persecution, makes an indelible impression on any who observe that life. This is why so much of the New testament is devoted to admonishing saints to reject worldly lusts, turn from lies, and live out a Christlike testimony.
Just as the testimony of a fully committed Christian is a powerful statement to the world, the testimony of a hypocritical and inconsistent lifestyle also sends a strong message, but not one of Good news. While it may be accurately pointed out how often in history God has used an unworthy testimony to get His point across to resistant ears, He has never condoned inconsistency or hypocrisy. Even if God uses a disobedient prophet, an unregenerated high priest, or a beast of burden to speak eternal truth into the world, the unstated yet synchronous message is not that God condones sin, but that God's grace is greater and overcomes even the worst unholiness.
We are all living epistles, "known and read by all men"; testimonies of Christ, "...written not with ink but by the Spirit of the living God, not on tablets of stone but on tablets of ... the heart." 2 Corinthians 3:2-3. The world is reading our epistle, (our letter of testimony), when they hear our voice, observe our conduct, and consider our ways.