‘Ga’, the 2nd letter, means ‘She Who grants all kinds of divine powers or siddhis and successes to human beings’. ‘La’, the 3rd letter, signifies ‘She That's the inspiration of a myriad of sustaining powers in the world such as earth which is Consciousness Herself’. You can find several reasons https://baglamukhi85174.bloggactif.com/36887069/a-secret-weapon-for-beej-mantra