Philosophy is about the love of knowledge, or the love of wisdom. Practically speaking, it is about the use of the rational mind, or logical mind, to find the basis or founding principles of anything we may want to talk about.
So, esoteric philosophy will be about exploring the basis or founding principles of anything we may want to talk about, while including the whole realm of what we call the esoteric or spiritual. Esoteric basically means “what is hidden”. What is understated here, “is what is hidden from the senses, from sensory reality, from sensory derived knowledge”. Our five senses are material, their range of perception, and so the knowledge that can be derived from them is limited to the sensory, phenomenal, and material reality. It is not their purpose to ascertain the reality of anything spiritual or esoteric.
Realities, such as the spiritual reality we call “the Soul”, are definitely outside of the realm of what sensory-derived knowledge can reach. It is therefore normal that the spiritual or the esoteric often seem non-existent, improvable, or difficult to know about. However, the spiritual can be touched, can be reached, when we realize what are the means to that end, and what are the obstacles in our path towards that goal. For that, the most important keyword and fundamental notion, will be that of “Consciousness”.