This paper presents two different views of the Neoplatonic mystical practice of union with the One through the philosophy of two representatives of Neoplatonism, Plotinus and Iamblichus. The purpose of the paper is to investigate two different ways of ascending to the One: Plotinus' dialectical path and Iamblichus' theurgical path, as well as the philosophical assumptions of such an ascent. The difference concerning the doctrine of the soul turns out to be crucial - with Plotinus, the soul always partly remains in the mind, while with Iamblichus, the whole soul is embodied and is in no way directly connected to the mind. The dialectical path implies the return of the soul to the mind through self-realization. It requires the preparation of the soul through dialectical education so that the soul is freed from attachment to this world and directs its attention to the sphere of the mind and beyond. In Iamblichus, dialectic is not sufficient to achieve the union of the soul with the One, therefore he establishes theurgy as a ritual practice that includes the summoning of deities into this world. He also considered it necessary to mediate between the soul and the mind, which resulted in further multiplication of the hypostases. This paper also investigates Porphyry's criticism of theurgical practices, as well as some of Iamblichus' counter-arguments against it.