Although missio Dei—the mission of God—has been a burning theme in missiology since the end of the twentieth century, a key verse, John 3:16, has been widely neglected in missiology until today. Yet, John 3:16 reveals missio Dei as the triune God’s salvific activities in the world and shows us the very motivation for missio Dei: God’s Radical Love, a love so vast, transcultural, and universal that no English words can translate the Hebrew. Three questions are explored herein: How does God’s Radical Love in John 3:16 justify God’s motivation for missio Dei as the work of the triune God in the Old Testament? What does God really plan to achieve in missio Dei? And how can missio Dei be applied by Christians in the twenty-first century? Based on his own experiences, the author specifically explores how Messianic Jewish congregations in Israel could respond to and participate in missio Dei, with the hope that thoughtful readers may apply this study to their own contexts, to engage their own congregations with a deeper understanding of God’s Radical Love in missio Dei.