To understand the difference between Christian and Atheistic equality, we must understand the difference between what I call “Christian progressivism” and “Atheist progressivism.”
Christian progressivism is the struggle to bring society in line with truth that God has revealed. The long history of Christian abolitionists who opposed slavery on the grounds that it is an affront to the laws of God is an example of Christian progressivism. Christian progressivism has been at the forefront of this type of social progress since Christianity’s inception (which means since the days of Judaism).
But when Christians fight for equality, human dignity, and love, it is to ensure that all Humans are empowered to fulfill the purposes that God has ordained (in scripture) for Human existence. So, the guiding force for Christian progressivism is the desire to serve, obey, and learn of God’s will for His children.
This means that Christian Progressivism pursues values such as equality within the framework of truth that God has revealed in scripture: the purpose of Human existence, gender roles, prohibitions on certain sexual behavior, etc. So, while treating Blacks as equal citizens helps society to better live up to Christian teachings about love and equality, instituting same-sex marriage or legalizing abortion may be contrary to the safeguards established by Christianity (God).
Atheistic progressivism is deceptively similar to Christian progressivism because it professes to retain Christian values such as equality, love, and human dignity.
But it rejects the idea that our pursuit of those values should be guided by either God or beliefs about human purpose, the immortality of the soul, or other transcendent truths (because, like God, none of these concepts can be scientifically studied or confirmed).
This has key consequences: While Christian Progressivism moves toward equality within the structured context of God’s revealed will, Atheistic Progressivism is free to reimagine equality outside of any meaningful restraint.
This is why the Atheist pursuit of equality leads to radical equality that seeks to eliminate differences in general.