The goddesses have a major role in both epics as Helpers of men. They have varied reasons for this.
             One is a maternal instinct. This is displayed in the literal mother-son relationships of Aphrodite and Aeneas, Thetis and Achilles, and the protective instinct that Athene displays in Book 3 of the Iliad when Pandarus arrow shot an arrow at Menelaus and she "took her stand in front and warded off the piercing dart, turning it just a little from the flesh, like a mother driving a fly away from her gently sleeping child" [p80]. Another motive of the goddesses is revenge. Athene and Hera are determined to destroy Troy to repay Paris for his Judgement when he "fell into the fatal error of humiliating the two goddesses... by his preference for [Aphrodite], who offered him the pleasures and penalties of love" [p438]. In the Odyssey, Athene's major motive for helping Odysseus often seems to simply be pity - such as in the speech she gives to Zeus at the beginning of book 5, p88.
             Some goddesses only help heroes because they have been ordered to do so by more powerful gods. Calypso agrees to let Odysseus go only when she is asked to by Hermes on behalf of Zeus.
             Goddesses might also help humans out of love, or sexual desire for them, as with Calypso and Circe. In the Iliad, Aphrodite who personifies sexual desire helps Paris, her favourite, so he can get back to Helen's bed and Aphrodite can revel in their lovemaking, which is an honour to her.
             Goddesses help men in the Iliad by making them more able to fight, such as the episode in Book 27 [p331] where Menelaus prays to Athene to help him, and in return she "strengthened his shoulders and his knees and planted in his breast the daring of a fly...", and Achilles' return to battle, where the goddess feeds him with divine food to sustain him in battle.
             Goddesses may help less able heroes in battle by removing them from the field, or disguising them. Aphrodite rescues Paris [p74] and Aen...