Col Dandridge McRae was commander of the "21st Arkansas Infantry Regiment" at this time. (a unit that as you may know was also called 3rd Battalion Arkansas Infantry, 15th Arkansas Infantry Regiment, and 15th (Northwest) Arkansas Infantry Regiment) The regiments and battery noted were obviously the units of Hebert's Brigade that Van Dorn carried to Corinth, most of which were probably the units that comprised Cabell's Brigade at the Second Battle of Corinth. Not all Arkansas regiments were carried to Corinth, at minimum the 16th Arkansas did not go.

You can look at an order of battle for Pea Ridge and for the Second Battle of Corinth to try to determine just who was there. As most Arkansas units in question changed designations once or twice in 1862-1863, I do not trust the Wikipedia OB information for Second Battle of Corinth, I have found at least one inaccuracy in it.

Without knowing what information you are trying to ascertain out of the message, I'd say that it is obvious that General Hebert is telling McRae to take charge of his brigade until he arrives, and to tell the Commanding General (Beauregard) that he (McRae) will be in charge of the brigade until that time. McRae was merely commander of the 21st, and left the regiment a few days after the "Siege of Corinth" to return to Arkansas to form a new regiment.