The second letter is from the Master and Wardens of Lodge No. 599 in Aughnacloy, Ireland stating that William Montgomery is a Master Mason, in good standing in their Lodge. It is attested to by the Lodge Secretary.
The first letter is from the Chapter of Royal Arch and Superexcellent Masons of the same Lodge stating that he is a Royal Arch and Superexcellent Mason of their Chapter. It also identifies him as a Past Master of Lodge No. 599.
You'll notice that the three Principle Officers and the Secretary of the Chapter are also the three Principle Officers and Secretary of the Lodge. At that time, Royal Arch Masonry was still part of "Regular" Lodges.
In a nutshell what these are is a document stating that William Montgomery is qualified to be a Royal Arch and Superexcellent Mason; and a document that says he is.
Aughnacloy is in what is now Northern Ireland, just north of the border with the Republic of Ireland.