"Fiery Gem, shining in all directions, do Thou burn up my dross, Oh Arunachala!"

             Five Hymns to Arunachala

In Talks, Sri Ramana Maharshi is being questioned concerning how to remove the obstacles (dross) within meditation.
                                                                    +++++++
 D.: Impurities of limitation, ignorance and desire (anava, mayika,
and kamya) place obstacles in the way of meditation. How to
conquer them?

M.: Not to be swayed by them.

D.: Grace is necessary.

M.: Yes, Grace is both the beginning and the end. Introversion (meditation) is due
to Grace: Perseverance is Grace; and Realization is Grace.

  "Significance of Om, unrivalled — unsurpassed! Who
can comprehend Thee, Oh Arunachala?"

                                                         Five Hymns to Arunachala
                        

            “The purport of prescribing meditation on the pranava (OM) is this. The Pranava is Omkara…the advaita-mantra which is the essence of all mantras such as Panchakshara. In order to get at this true significance, one should meditate on the Pranava. This is meditation which is of the nature of devotion consisting in reflection on the truth of the Self. The fruition of this process is samadhi which yields release moksha  [liberation from all aspects of mental dross, ed. note], which is the state of unsurpassable bliss.”

        (Collected Works of Ramana Maharshi, 6th edition, Self Enquiry #28 p. 23-24)