I'm no expert on Middle Irish, but I do know modern Irish. If we assume the ME text given as correct, then "a meic dil Dé" is "a mhic dhil Dé" not "a Mhic ghil Dé" - dil means dear/beloved, gil(geal) means bright - it's easy to confuse them because they both sound the same.

For those grammar-minded, "tuc" (give) is "tabhair" in modern Irish, which seems odd, but the past tense of "tabhair" is "thug" which reflects the original Middle Irish.

"seirc/serc" (love) is "searc" in modern Irish (I've seen some posting spelled "search" which is wrong).

As for pronunciation of the Middle Irish, the consonants change sound based on the function of the word and the position in the sentence. Modern Irish shows this by adding "h" after the initial letter, but the ancients just "knew".