Genesis 18:1 says, And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day;  God appeared to Abraham once again as Abraham was going about his everyday life.  God does not meet us at specific places at specific times, but if we are followers of Christ He is with us everywhere we go.  We simply have to recognize when God speaks to us.  Verse two states,  And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground,  When Abraham looked up, he saw three men and ran to meet them and bowed before them.  We may need to look up at times to see what God would have us do, and we should always do so humbly.  Verse three adds, And said, My Lord, if now I have found favour in thy sight, pass not away, I pray thee, from thy servant:  For whatever reason, Abraham recognized these three men as being more than just men, but as beings sent by God, and he asked them not to pass him by.  We need to look beyond the obvious sometimes to see God at work in our lives.  Verse four continues, Let a little water, I pray you, be fetched, and wash your feet, and rest yourselves under the tree:  Then verse five concludes, And I will fetch a morsel of bread, and comfort ye your hearts; after that ye shall pass on: for therefore are ye come to your servant. And they said, So do, as thou hast said.  Abraham asked them to stay and let him provide them with food and comfort and they agreed to stay.  We cannot force God, or His messengers to come and fellowship with us, but we should always invite them to.  We may not always recognize God's messengers by their appearance, so we should be hospitable to all people who come our way.  Verse six says, And Abraham hastened into the tent unto Sarah, and said, Make ready quickly three measures of fine meal, knead it, and make cakes upon the hearth.  Verse seven adds, And Abraham ran unto the herd, and fetcht a calf tender and good, and gave it unto a young man; and he hasted to dress it.  Then verse eight concludes,  And he took butter, and milk, and the calf which he had dressed, and set it before them; and he stood by them under the tree, and they did eat.  Abraham didn't just give them what was already prepared, but went out of his way to provide a feast for them.  We should always be willing to do extra to meet the needs of those around us, whether they are heavenly beings or just normal people.  Verse nine asks, And they said unto him, Where is Sarah thy wife? And he said, Behold, in the tent.  The men asked where Sarah was and Abraham told them she was in the tent.  At least Abraham didn't try to claim that she was his sister.  We need to be truthful with God and His messengers.  Verse ten says, And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.  One of the men said that he would certainly return to Abraham and that Sarah would have a son.  This man was speaking as a representative of God, and it was God Himself who would bring this about.  We can only speak for God, and we cannot do things that God alone can accomplish.  Verse eleven states, Now Abraham and Sarah were old and well stricken in age; and it ceased to be with Sarah after the manner of women.  Abraham and Sarah were both past child bearing age, though this would be especially true of Sarah.  Verse twelve adds, Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?  Sarah laughed and still questioned God's promise.  We must never question what God has promised us, no matter how impossible it may seem.  Verse thirteen declares, And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?  We know that this was God Himself, or the LORD, speaking to Abraham.  He asked Abraham why Sarah laughed.  Then verse fourteen asks, Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.  We need to ask ourselves the same question whenever God asks us to do something that seems impossible.  Verse fifteen states, Then Sarah denied, saying, I laughed not; for she was afraid. And he said, Nay; but thou didst laugh.  Sarah denied laughing, but was told that she indeed did laugh.  It does us no good to deny it when we doubt God.  He already knows when we do.