Second line: ॐ ह्रीं श्रीं auṁ hrīṁ śrīṁ ॐ used at the beginning of the first line of the mantra refers to the Supreme Self, known as Brahman. The ॐ here in the second line represents the individual being. Thus, this ॐ is to be replaced with ātma-bīja, which is given by one’s guru at the time of initiation. Everyone will have ātma-bīja, which is derived based on several factors. Ātmabīja is discussed here. In case one’s guru has not given any ātma-bīja to an aspirant, he can continue to use ॐ as his ātma-bīja. ātma-bīja Is explained here: http://manblunder.com/articlesview/how-to-derive-atma-bija The three bījas used here refers to three stages. ॐ is apara stage or the individual soul. Hrīṁ represents the union of Śiva and Śakti and is known as parāpara (the stage of cause and effect). The last bīja, śrīṁ is the stage of para, the Supreme energy, the state of Supreme Paramaśiva, where Śakti stands merged with Śiva. In this stage, She cannot be identified as a separate entity. For attaining liberation, one has to merge into Paramaśiva. In other words, the individual soul (ॐ) transcends māyā, which is represented by hrīṁ, where both Śiva and Śakti are present as separate energies. The aspirant goes past māyā through practicing sādhana, represented by bīja hrīṁ, to merge with the Supreme Self, represented by the third bīja, śrīṁ. Thus in the second line of mahāṣoḍaśī-mantra, liberation is explicitly declared. The third, fourth and fifth lines are Pañcadaśī-mantra (15 bījas) as explained in the next videos. In sixth and last line the bījas of the first line are placed in a reverse order. This is known as mantra-sampuṭīkaraṇa. This means that the three bījas of the second line, and the Pañcadaśī-mantra are enclosed by the first line (forward) and the last line (reversed), so that effects of Pañcadaśī-mantra and the bījas of the second line do not go out of the aspirant and are sealed within him.