I came out of protestant Christianity not being able to believe some stuff in the Bible, was an atheist for a while, but mindful that I had spiritual/paranormal experiences at times in the past, so I kept searching for the truth. I found a Buddhist friend on the internet who taught me all about Buddhism, especially Vajrayana and Dzogchen (yeah I was "lucky") but he understands all vehicles very well. Concurrently, I actually listened to an atheist podcast and one of the episodes had a Buddhist as a guest who explained Madhyamaka and I was blown away (so was the host). His intent was to explain selflessness (of persons and objects) to "logical" atheists in a way that would be convincing to them. He used a lot of thought experiments, some very sci-fi ones. It worked for me.
To develop bodhichitta, which is the actual practice, you need to develop such compassion that you simply cannot bear others being tormented by suffering. But in order to develop this compassion, you must know exactly how you yourself are plagued by suffering. And you must understand that the whole of samsara is by nature suffering. But first you must fear the lower realms, for without this you will have no repudiation of celestial and human happiness. You must therefore train your mind in the small- and medium- scope parts of the path. -- Pabongka Rinpoche