Thelema is the will. Part of it is about doing the entire ritual in the mind instead of physically. It's like the analogy of the group who visualized throwing basketball into the hoop compared to the group which practiced physically. Both did their mental/physical training respectively for 30 days. In the end, there was only slight different between their results. But both groups had significant improvement compared to another group which did no practice at all.
Thelema means to do magick in a way that is purely mental. All of magick is about using the Will and the Imagination. Both are right brain faculties, compared to Reason and Logic of the Left brain.
The essence of magick is thelema. That does not mean one should not do ritual, because ritual can be used for the purpose of assisting thelema. Ritual done by itself has no meaning. All ritual is meant to serve thelema. After all, the definition of magick is the act of causing change in accordance with Will.
For Ritual and Psionics there is a little difference. To personally use "magick" is also to refer to any kind of phenomena you cause or affect using a much deeper part of yourself than some do for psionic work. For psionics, you use your pre-conscious and sub-conscious minds (or parts of the mind) with suggestion or action; for "magick," you use something deeper. Your soul as inner energy to power the calling of the active force and elemental energy, as the active force with a directive will by the soul.
Except to some they are the same energy, just that they are charged differently
and magic uses the soul. Where psionics use the sub-conscious. When you use magic ritual, you cause a negative drawing force and when you use psionics you can cause a push force that causes effects. So in essence, magic uses everything that psionics does and more.
Psionics is more pure mind force in technique. Although a more encompassing psionic theory also goes into a lot of magickal stuff.