Which metaphysical commitments draw Raja Yoga (the path of willpower and concentration) together with Advaita Vedanta (the path of knowledge)?

In Meditation and Its Practices: A Definitive Guide to Techniques and Traditions of Meditation in Yoga and Vedanta, Swami Adiswarananda tells us that there are four such principles–namely, the “divinity of the individual soul, [the] unity of existence, [the] oneness of Ultimate Reality, and [the] harmony of religions” (xi).

The first principle states that within the individual person resides the indwelling Self. One should reflect upon this principle. Behind the physical body, the energy body, the mental body, the intellectual body, and the bliss body, is there, indeed, a Self that is luminously and changelessly aware?

The second could be cast slightly more precisely by saying that there’s a unity to all appearances. Whatever it is that appears is actually the Self.

The third states that while the names of Ultimate Reality are many, the essence is one. Some call the Ultimate “God” while others refer to it as “Brahman.” Ultimately, these names–and many others besides–are pointing to the same, undeniable, invariable Reality. As The Daodejing says, “Names that can be named are not the Eternal Name.” And the Eternal Name is not a name.

The last–very perennialist–is quite loving in that it urges us to see all religions as essentially pushing toward, and ultimately converging upon, the same first three principles. A longer discussion, of course, would be necessary in order to make plain how the “mystical kernel” in all (perennialists will qualify this word “all” by adding in “orthodox”) religions is the Oneness of Being.

Advaita Vedanta in particular very lovingly accepts all paths to the Truth–most especially dualist and qualified nondual paths. We should be so compassionate by taking the longest view of why we’re all here.