And when he saw them, he ran to meet them from the tent door, and bowed to the ground (Gen. 18:2
The great Sage Shammai said: "Greet every man with a pleasant countenance." Should a person give his friend every gift in the world, yet greet him with a scowl, it is considered as if he gave him nothing. But if he greets him with a smile, it is considered as if he gave the other person everything, even if he is empty-handed. (Avot D'Rabbi Natan)
And he took butter and milk and the calf which he had prepared and set it before them (Gen. 18:8)
How could Abraham have offered his guests meat and milk at the same time? The answer is that he served the meat and dairy foods to them separately, with the intention that each guest should choose for himself what he wished to eat. Abraham even went to the trouble of preparing three tongues, should each of the three guests wish to eat only meat. This is the epitome of the mitzva of hospitality (Likutei Sichot)
And offer him there for a burnt offering (Gen. 22:2)
"Master of the Universe!" cried Abraham before G-d. "When you commanded me to offer up my son as a burnt offering, I could have said, 'But yesterday You promised that my seed would be perpetuated through Isaac!' However, I conquered my own inclination to carry out Your will. In return, may it be Your will that should the descendents of Isaac ever be in trouble, with no one to defend them, You Yourself will come to their defense." (Jerusalem Talmud, Taanit)