What does Genesis 24:18 mean?

In the previous verse, Abraham's servant approached Rebekah, asking for a drink of water. His plan, according to his prayer to God, is that one of the women at this well will respond to this request by offering to also bring water for the servant's ten camels (Genesis 24:12–14). This is no small task, so such a favor would suggest a woman of high character. The servant intends to pursue the woman this test signifies; she is, presumably, the one God intends to be brought bring back as a wife for Isaac, son Abraham.

Before the servant had even completed his prayer, an attractive woman appears, and he decides to put into effect his plan to find the girl God has appointed for Isaac. So the servant asked her for some water to drink.

Here, she responds by "quickly" giving him a drink from her jar. The emphasis on her immediate reaction is meant to show Rebekah's generosity.