Whitefield was a staunch Calvinist so such a view would be expected to be the foundation of his views on salvation. Athough, this is a "basic Christianity" issue and Christiandom has been uniform in this belief for 2000 years for the most part.
My simple explanation is that Christianity is all about the free will to trust in God but its also about the free will to suffer the consequences of turning away from God.
Free will does not survive collectivism.