It's simple. Craig and Tess sense the call of God upon their lives to go and proclaim the Gospel of Jesus Christ. As a child, Craig grew up in ministry, and never really stopped singing and ministering but this is different. Deep down, He and his wife have had a sense of urgency compelling them to take steps of faith like never before, and God has been bringing them both to a place of total dependence upon Him. Jesus Christ has rescued them and changed their lives, and they want to spend the rest of their lives compelling others to come to the saving arms of Christ. A portion of scripture that was laid upon their hearts, as sort of a mission statement for their marriage, is Isaiah 58. These words are a beautiful picture of what it looks like to live out the Gospel of Jesus, and the reason they've followed God into the ministry of evangelism.
“Is not this the fast that I choose: to loose the bonds of wickedness, to undo the straps of the yoke, to let the oppressed go free, and to break every yoke?… If you pour yourself out for the hungry and satisfy the desire of the afflicted, then shall your light rise in the darkness and your gloom be as the noonday. And the LORD will guide you continually and satisfy your desire in scorched places and make your bones strong; and you shall be like a watered garden, like a spring of water, whose waters do not fail. And your ancient ruins shall be rebuilt; you shall raise up the foundations of many generations; you shall be called the repairer of the breach, the restorer of streets to dwell in." -from Isaiah 58