Jeremy Simms delivers a Christmas gift to Stacey. Why does David Logan then try to discourage Stacey from calling Jeremy a friend?

In Chapter Seven, Jeremy Simms arrives at the door and gives the family some nuts and Stacey a flute that he carved himself. Stacey cannot understand why Jerermy brought him a gift until Papa suggests he gave Jeremy the gift of friendship in the past year. But Papa warns him that friendship between a black man and white man can never be on an equal basis and it would cost too much to find out if this friendship with Jeremy could last.