I was wondering about this and thinking what I would say if an atheist were to question me on why this is. 

If you really think about it, why is it like this? Why do we "love God" or are on His good side etc. only if we do what He wants us to do? 

You prove your love or care for anyone by actually being good to the person and doing things etc., not by obeying them like a slsve, but you can't really do this with God because there's nothing you can really do for Him, except just obey for obedience's sake, but why? 

I was wondering about this and thinking what I would say if an atheist were to question me on why this is.

If you really think about it, why is it like this? Why do we "love God" or are on His good side etc. only if we do what He wants us to do?

You prove your love or care for anyone by actually being good to the person and doing things etc., not by obeying them like a slsve, but you can't really do this with God because there's nothing you can really do for Him, except just obey for obedience's sake, but why?

Jesus Himself has the answer to your question in Chapter 14 of the Gospel of St John:

[21] He that hath my commandments, and keepeth them; he it is that loveth me. And he that loveth me, shall be loved of my Father: and I will love him, and will manifest myself to him. [22] Judas saith to him, not the Iscariot: Lord, how is it, that thou wilt manifest thyself to us, and not to the world? [23] Jesus answered, and said to him: If any one love me, he will keep my word, and my Father will love him, and we will come to him, and will make our abode with him.

And in John 15.15:

"I will not now call you servants: for the servant knoweth not what his lord doth. But I have called you friends: because all things whatsoever I have heard of my Father, I have made known to you."

We obey not from servitude, or to get on His "good side", but because He first loved us, we respond to His Love. We obey, not for "obedience sake" but for Love's sake.

Do you read the Gospels?