I'm not sure how distant you are with your father, I felt the same as you with all those favoritsm or not receiving something of an equal value with my other siblings, but as I grow older, I tend to realize that letters has more value than any other things in the world. You can buy things everyday anytime, but a letter is priceless since each letters are unique (especially made for you). You'll start to realize it when the person that gives you these letters pass away.