This is confusing.
In your OP your talked of deleting rows in Sheet1. When there is no sheet tab name "Sheet1" nor even a VBA code name Sheet1 then can you see how confusing it can be.
Your two sheets' tab names are "50258 sample" and "Result" It's reasonable to assume in the absence of you clearly defining sheet 1, that you meant it to be the first shown tab name going left to right, i.e. the "50258 sample" sheet. That sheet has a VBA code name "sample_sheet"
I interpreted the "Result" sheet is what you want the 50258 sheet to look AFTER the rows have been deleted from the 50258 Sample sheet. It's even more confusing since you mention a Sheet 3 which doesn't exist.
Hence my VBA code deletes the rows in the 50258 Sample sheet. See the With block of code
where column G has been added and identifies which values on the 50258 sheet don't exist.
All that said you appear to be saying that the rows that are currently being deleted should remain and the others remain. In which case just change the first line of code in the With block to
.Range("G2:G" & lLastRow) = "=IF(MATCH(C2,Result!C:C,FALSE)>0,""Delete"")"
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