Due to the relational nature of nursing, “being with” the person being cared for is an essential phenomenon in the nursing profession. Furthermore, this concept lies at the very core of the philosophy of caring, which is, according to various authors, the essence of nursing. Using Watson’s Human Caring philosophy as its disciplinary perspective, this phenomenological study has explored, with nurses working in rehabilitation (n = 17), the meaning of the experience of “being with” the person cared for, as well as the nurses’ perception of the contribution of this experience to the rehabilitation of the person cared for. A total of 51 interviews, three for every participant, were analyzed using the Relational Caring Inquiry phenomenological method developed by Cara (1997). Through data analysis, five eidos-themes emerged. The first four related to the significance of “being with” the cared-for person: the importance of humanistic values at the core of care; the involvement of the nurse and the person cared for; the reciprocal and relational dimensions of care; and the irreplaceable care experience of contextual complexity. The fifth and final eidos-theme—enhancing the body-soul-spirit harmony of the person cared-for and of the nurse—leads participants to perceive the therapeutic contribution of the experience of “being with” the person cared for during their rehabilitation process. These results have contributed to the emergence of the meaning of the phenomenon studied: “a deep, therapeutic, and transforming human relationship.” All the results lead to innovative implications and suggest possible interventions that can serve as guides to renew the clinical practice of nurses in rehabilitation, as well as education and research in nursing science.