Why did Bolivar call Father Bartolomé de las Casas "The Apostle of America"?

The Spaniard Roman Catholic priest Bartolome de las Casas was the famous defender of American Indians rights,and he was also the one who suggested to Spain to use Africans instead of American indians as slaves.He is often called the "Apostle' since his liberal & linient attitude towards the non Roman catholic & non believer American Indians, sometimes went against the strict Roman Catholic colonial laws.There exists a statue in Sevile or Madrid,Spain that depit Bartolome de las casas standing and a male American Indian on his knees pleading for savior and mercy.