Allow me to anticipate an objection you might have to this clip.
Objection: “Mike’s answer depends on God’s existence and he hasn’t proven that yet.”
Response: This question completely depends on the hypothetical that “if Christianity is true then…”. The question is only useful if it allows that the nature of the difference between atheism and theism be the REASON why a moral act can be performed by a theist which an atheist cannot do. To object to my answer on the basis that it stands on the difference between atheist and theist beliefs is to object to the question itself and not my answer. You can’t have your cake and eat it too. Either this question grants a real difference in worldview approaches or it is a useless rhetorical trick. The framing of the question requires that we either grant God’s existence for the answer or we ditch the question as trickery.
Another Christian answered this question quite well, long before I did. Though I don’t recall it specifically, I imagine I saw this video at some point and it may have influenced my own thoughts without me remembering. Either way, the answer is ultimately based on the teachings of Jesus, which means that Jesus laid the groundwork for this answer 2000 years ago. https://www.youtube.com/watch?v=qqt3Ie8l-fo
My website https://BibleThinker.org