If you're reconciling two sheets, you shouldn't merge them.
What I normally do in this case is to make sure that the ID number is in the left-hand column both both ranges, and then name each range with something pithy that has meaning. Then, on a third sheet, copy both lists of ID numbers into the same column. You can then use the advanced filter option to filter the combined list in place, just retaining unique values. This gives you a complete list of all the ID numbers.
Finally, use the IF, ISERROR and VLOOKUP formulae to determine which values are unique to one or the other sheet, and which are common to both.
Also, this isn't an instant help service. Everyone who posts here is volunteering their time, and might not be able to check every day