Fear based religion is a contradiction. They preach about the "love of God" while threatening "eternal damnation" if you don't comply. That is a form of cognitive dissonance. Rational people understand that doing what is right is good and doing what is wrong will have very real consequences in this life. There is no need for any religious threat to make them into "good" people.
But again the question I posed to the OP. How do you know what is good?
The Golden Rule!
And no, that is not the property of religion. Besides the fact that it is in every religion it is also the standard by which society operates.
Golden Rule didn't come from Christianity. It's actually found in many different religions, though as a Jew, Jesus was quoting the version in Judaism.
Love and Brotherhood
26. To love all human beings who are of the covenant (Lev. 19:18) (CCA60). See Love and Brotherhood.
27. Not to stand by idly when a human life is in danger (Lev. 19:16) (CCN82). See Love and Brotherhood.
28. Not to wrong any one in speech (Lev. 25:17) (CCN48). See Speech and Lashon Ha-Ra.
29. Not to carry tales (Lev. 19:16) (CCN77). See Speech and Lashon Ha-Ra.
30. Not to cherish hatred in one's heart (Lev. 19:17) (CCN78). See Love and Brotherhood.
31. Not to take revenge (Lev. 19:18) (CCN80).
32. Not to bear a grudge (Lev. 19:18) (CCN81).
33. Not to put any Jew to shame (Lev. 19:17) (CCN79).
34. Not to curse any other Israelite (Lev. 19:14) (by implication: if you may not curse those who cannot hear, you certainly may not curse those who can) (CCN45).
35. Not to give occasion to the simple-minded to stumble on the road (Lev. 19:14) (this includes doing anything that will cause another to sin) (CCN76).
36. To rebuke the sinner (Lev. 19:17) (CCA72).
37. To relieve a neighbor of his burden and help to unload his beast (Ex. 23:5) (CCA70). See Love and Brotherhood.
38. To assist in replacing the load upon a neighbor's beast (Deut. 22:4) (CCA71). See Love and Brotherhood.
39. Not to leave a beast, that has fallen down beneath its burden, unaided (Deut. 22:4) (CCN183). See Love and Brotherhood.
Judaism 101 A List of the 613 Mitzvot Commandments