My image is rejected..need input please

Hi…I’m new to this forum and new to submitting my images to Envato as well.

I’ve submitted an image (it’s a collection of icons with a heart theme). I’m not quite sure why it got rejected, because I got the reply “it isn’t at the quality standard required to move forward”
I’m not quite sure what does it mean. Is my image not good enough or did I do wrong with the file or something else ?

And also there’s a note that “you won’t be able to re-submit this item again”.
What does it means ? even though I make the revision, I can’t re-submit it again ?

Any kind of feedback will be very helpful.

Thank you very much