| Quote #1
At last Louis XIII made Tréville the captain of his Musketeers, who were to Louis XIII in devotedness, or rather in fanaticism, what his Ordinaries had been to Henry III, and his Scotch Guard to Louis XI. (2.3)
Being one of the King’s Musketeers, then, means that you must have instant and automatic devotion to the King.
| Quote #2
This short interval was sufficient to determine D’Artagnan on the part he was to take. It was one of those events which decide the life of a man; it was a choice between the king and the cardinal--the choice made, it must be persisted in. (5.75)
As we know, D’Artagnan chooses to side with the King. This moment cements his loyalties forever; note that he didn’t take time to think about it or make little charts of the Cardinal vs. the King on all the various issues. D’Artagnan just makes a choice and loyally sticks with it.
| Quote #3
"Well," replied the cardinal, who could not for an instant suspect the loyalty of Tréville, and who felt that the victory was escaping him, "well, but Athos was taken in the house in the Rue des Fossoyeurs." (15.45)
Tréville’s loyalty is so well-established that his word is impossible to challenge. D’Artagnan, in using Tréville as an alibi, takes advantage of Tréville’s well-known loyalty to the King.