The purpose of Brexit depends on who you ask.
The purpose, from the perspective of the wealthy, is to get rid of the meddling Europeans and their bizarre commitment to laws that restrict the ability of the wealthy to plunder the nation without restraint.
The purpose, from the perspective of the Brexit voters, is to get rid of Johhny Foreigner, so the Great Britain can be transformed back into the glorious empire that bestrode the world, as it did in the mid-1950s, when the sun always shone, we played cricket on the village green, and had scones and jam for tea.
Of course, the latter is total and abject nonsense in every respect; but it is popular, and it achieves the goals of the former, so it doesn't need to be in any way connected to reality.