双FOR循环需要一段时间才能完成

I need to compare 2 cells in different sheets and get a value if there's a match. I currently have this piece of code, it each cell in column B is checked to each cell in column A and if there's a match the corresponding cell in column C is copied. So far so good, the problem is, it takes a long time to do so. I only have 750 records in column B and 4000 in column A.I need to compare 2 cells in different sheets a