He's earned/obtained 1st string status. This is not a hard concept.
An engineering firm can't hire a new engineer for nothing (or below market value) and tell him/her that they will pay appropriately when they prove worthy of the pay. A company cannot promote an internal candidate to manager/director without a pay increase, stating instead that they will consider paying the person the appropriate manager/director rate once he/she has established over a year or so to be worthy of that pay.
One of the other sports sites intimated that Merklinger will be paid 6 figures (100,000-999,999). If true, and if Merklinger earns the starter role, that pay rate will likely be the biggest bargain for the QB position in the SEC.