Oberon had Puck annoint Titania's eyes because he wanted to make her look foolish as she fell in love with whomever or whatever she saw upon waking. He got his wish when she awoke and saw Bottom with his ass's head, then promptly fell in love with him. Oberon wanted Titania to look foolish because he was angry with her when she wouldn't give up the changeling child who was currently receiving all her attention. Titania said the child had belonged to a votress of hers (a lady in waiting) who died and upon the lady's death had promised to care for the child. Oberon was jealous of the attention the child was getting and he wanted Titania to give over the child to him, but she refused. Oberon figured that if Titania's attention was distracted by being in love, he could get the child from her and his plan worked. Since Oberon had the changeling child, he no longer needed Titania to be in love with Bottom, so he annointed Titania's eyes again and when she awoke, it was Oberon that Titania saw. Their relationship was once again loving.