20 The word “take” is supplied in the translation for stylistic reasons. In the Hebrew text the sentence lacks a verb other than the imperative “hurry.” The elliptical structure of the language reflects Abraham’s haste to get things ready quickly.
21 Three measures (Heb “three seahs”) was equivalent to about twenty quarts (twenty-two liters) of flour, which would make a lot of bread. The animal prepared for the meal was far more than the three visitors needed. This was a banquet for royalty. Either it had been a lonely time for Abraham and the presence of visitors made him very happy, or he sensed this was a momentous visit.
22 The bread was the simple, round bread made by bedouins that is normally prepared quickly for visitors.

In other versions

And Abraham went quickly into the tent to Sarah and said, “Quick! Three seahs of fine flour! Knead it, and make cakes.”

So Abraham hurried into the tent to Sarah. “Quick,” he said, “get three seahs of the finest flour and knead it and bake some bread.”

So Abraham hurried into the tent and said to Sarah, “Quick! Knead three measures of fine flour and make bread.”

So Abraham ran back to the tent and said to Sarah, “Hurry! Get three large measures of your best flour, knead it into dough, and bake some bread.”

Then Abraham hastened into the tent to Sarah, and he said, “Quickly—make three seahs of fine flour for kneading and make bread cakes!”

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.

Public Domain