Catechism of the Catholic Church

Because Abraham believed in God and walked in his presence and in covenant with him, the patriarch is ready to welcome a mysterious Guest into his tent. Abraham's remarkable hospitality at Mamre foreshadows the annunciation of the true Son of the promise. After that, once God had confided his plan, Abraham's heart is attuned to his Lord's compassion for men and he dares to intercede for them with bold confidence. (494, 2635)