I've shared before a list with the many benefits of breastmilk, but sometimes a visual aid helps!
Here are two photos of milk pumped for the same baby at different ages - the yellow one from the week he was born, the white from a couple months of age. As you can see the difference in color (due to fat content) is significant, and the yellow milk is in part due to the change from colostrum to straight milk:
Isn't that amazing? And just for fun a photo of the squishy baby who grew so plump thanks to that breastmilk: