Different scholars have different views regarding the origin of the graphic form of letter Կ. As its prototype, they consider the Armenian letter Գ [g], as well as several letters of the Greek, Syrian, and Iranian alphabets. In the opinion of linguist Eduard Aghayan, Կ is an “intermediate form created by correlation of three forms – the Greek, Syrian and Iranian”. In Grabar, the Old Armenian language, կ stood for a sound that conformed to the Russian [к]. Of the two New Armenian literary languages, only the Eastern Armenian inherited this sound, while in the Western Armenian կ has retained its traditional way of writing, but now it denotes sound [g]: կարմ իր ([garmir] – red), կրակ ([grag] – fire), Կիրակոս ([Giragos] – Kirakos), Կարապետ ([Garabed] – Karapet), etc.
In general, the literary Eastern Armenian language has preserved the phonetic system of Grabar much more than the literary Western Armenian, which has gone through the so-called “consonant shift”. In the grammatical structure of the Armenian language, կ denotes a verbal particle. In manuscripts that date back to XII century it is sometimes written as կու. In Grabar, this particle did not exist, and its emergence itself signifies development of a new, Middle Armenia language – intermediary between the Old and the New Armenian. Particle կ is used both in the Eastern and Western Armenian – in the former it denotes the future tense (կգրեմ [kgrem] – I will write), in the latter – the present tense (կը գրեմ [kә grem] – I write).
See more at Aram Khachaturians "Armenian Alphabet. History and Symbolism" book