Why has Saudi Arabia been welcomed into the UN's Human Rights Council ?

Saudi Arabia  a country with appalling notorious woeful reputation  for human rights abuses has been welcomed to the UN Human rights council, facilitated in part by our own PM, David Cameron, has himself looked at curtailing many of our own personal freedoms, indeed he has already eroded many. I think I see a pattern emerging.
Saudi Arabia continues to try convict and imprison political dissidents and human rights activists solely on account of their  peaceful activities. Still subjecting hundreds of people to unfair trials and arbitrary detentions. People  daily being curtailed carrying   out  their beliefs. Saudi Arabian judges routinely sentence detainees to floggings with hundreds of lashings, the use of torture an every day occurrence. Women's rights  hardly in existence at all.
It is a mockery of humanity, when  a country that carries out  cruel inhuman punishments, that shackles its media, who in the last 20 years  has had over 2,000  people executed can be welcomed  by the UN in this way.  last year alone 175 people executed, for crimes that were hardly capitol offences. Saudi Arabia executes more people than any other country except China and Iran.
But the fact  that Saudi Arabia sits on the  world's largest  reserves of oil, could have been a contributing factor.
This decision by the UN  mocks the pain off dissidents currently languishing in Saudi Jails.