Iso mantra 18

agne naya supathā rāye asmān
viśvāni deva vayunāni vidvān
yuyodhy asmaj juhurāṇam eno
bhūyiṣṭhāṁ te nama-uktiṁ vidhema
Synonyms: 
agne — O my Lord, as powerful as fire; naya — kindly lead; supathā — by the right path; rāye — for reaching You; asmān — us; viśvāni — all; deva — O my Lord; vayunāni — actions; vidvān — the knower; yuyodhi — kindly remove; asmat — from us; juhurāṇam — all hindrances on the path; enaḥ — all vices; bhūyiṣṭhām — most numerous; te — unto You; namaḥ uktim — words of obeisance; vidhema — I do.
Translation: 
O my Lord, as powerful as fire, O omnipotent one, now I offer You all obeisances, falling on the ground at Your feet. O my Lord, please lead me on the right path to reach You, and since You know all that I have done in the past, please free me from the reactions to my past sins so that there will be no hindrance to my progress.
Purport: 

By surrendering to the Lord and praying for His causeless mercy, the devotee can progress on the path of complete self-realization. The Lord is addressed as fire because He can burn anything into ashes, including the sins of the surrendered soul. As described in the previous mantras, the real or ultimate aspect of the Absolute is His feature as the Personality of Godhead, and His impersonal brahma-jyotir feature is a dazzling covering over His face. Fruitive activities, or the karma-kāṇḍa path of self-realization, is the lowest stage in this endeavor. As soon as such activities even slightly deviate from the regulative principles of the Vedas, they are transformed into vikarma, or acts against the interest of the actor. Such vikarma is enacted by the illusioned living entity simply for sense gratification, and thus such activities become hindrances on the path of self-realization.

Self-realization is possible in the human form of life, but not in other forms. There are 8,400,000 species, or forms of life, of which the human form qualified by brahminical culture presents the only chance to obtain knowledge of transcendence. Brahminical culture includes truthfulness, sense control, forbearance, simplicity, full knowledge and full faith in God. It is not that one simply becomes proud of his high parentage. Just as being born the son of a big man affords one a chance to become a big man, so being born the son of a brāhmaṇa gives one a chance to become a brāhmaṇa. But such a birthright is not everything, for one still has to attain the brahminical qualifications for himself. As soon as one becomes proud of his birth as the son of a brāhmaṇa and neglects to acquire the qualifications of a real brāhmaṇa, he at once becomes degraded and falls from the path of self-realization. Thus his life's mission as a human being is defeated.

In the Bhagavad-gītā (6.41-42) we are assured by the Lord that the yoga-bhraṣṭas, or souls fallen from the path of self-realization, are given a chance to rectify themselves by taking birth either in the families of good brāhmaṇas or in the families of rich merchants. Such births afford higher chances for self-realization. If these chances are misused due to illusion, one loses the good opportunity of human life afforded by the almighty Lord.

The regulative principles are such that one who follows them is promoted from the platform of fruitive activities to the platform of transcendental knowledge. After many, many lifetimes of cultivating transcendental knowledge, one becomes perfect when he surrenders unto the Lord. This is the general procedure. But one who surrenders at the very beginning, as recommended in this mantra, at once surpasses all preliminary stages simply by adopting the devotional attitude. As stated in the Bhagavad-gītā (18.66), the Lord at once takes charge of such a surrendered soul and frees him from all the reactions to his sinful acts. There are many sinful reactions involved in karma-kāṇḍa activities, whereas in jñāna-kāṇḍa, the path of philosophical development, the number of such sinful activities is smaller. But in devotional service to the Lord, the path of bhakti, there is practically no chance of incurring sinful reactions. One who is a devotee of the Lord attains all the good qualifications of the Lord Himself, what to speak of those of a brāhmaṇa. A devotee automatically attains the qualifications of an expert brāhmaṇa authorized to perform sacrifices, even though the devotee may not have taken his birth in a brāhmaṇa family. Such is the omnipotence of the Lord. He can make a man born in a brāhmaṇa family as degraded as a lowborn dog-eater, and He can also make a lowborn dog-eater superior to a qualified brāhmaṇa simply on the strength of devotional service.

Since the omnipotent Lord is situated within the heart of everyone, He can give directions to His sincere devotees by which they can attain the right path. Such directions are especially offered to the devotee, even if he desires something else. As far as others are concerned, God gives sanction to the doer only at the risk of the doer. But in the case of a devotee, the Lord directs him in such a way that he never acts wrongly. The Śrīmad-Bhāgavatam (11.5.42) says:

sva-pāda-mūlaṁ bhajataḥ priyasya
tyaktānya-bhāvasya hariḥ pareśaḥ
vikarma yac cotpatitaṁ kathañcid
dhunoti sarvaṁ hṛdi sanniviṣṭaḥ

"The Lord is so kind to the devotee who is fully surrendered to His lotus feet that even though the devotee sometimes falls into the entanglement of vikarma-acts against the Vedic directions—the Lord at once rectifies such mistakes from within his heart. This is because the devotees are very dear to the Lord."

In this mantra of Śrī Īśopaniṣad, the devotee prays to the Lord to rectify him from within his heart. To err is human. A conditioned soul is very often apt to commit mistakes, and the only remedial measure to take against such unintentional sins is to give oneself up to the lotus feet of the Lord so that He may guide one to avoid such pitfalls. The Lord takes charge of fully surrendered souls; thus all problems are solved simply by surrendering oneself unto the Lord and acting in terms of His directions. Such directions are given to the sincere devotee in two ways: one is by way of the saints, scriptures and spiritual master, and the other is by way of the Lord Himself, who resides within the heart of everyone. Thus the devotee, fully enlightened with Vedic knowledge, is protected in all respects.

Vedic knowledge is transcendental and cannot be understood by mundane educational procedures. One can understand the Vedic mantras only by the grace of the Lord and the spiritual master (yasya deve parā bhaktir yathā deve tathā gurau [ŚU

Hearing and chanting the glories of the Lord is itself an act of piety. The Lord wants everyone to hear and chant His glories because He is the well-wisher of all living entities. By hearing and chanting the glories of the Lord, one becomes cleansed of all undesirable things, and then one's devotion becomes fixed upon the Lord. At this stage the devotee acquires the brahminical qualifications, and the effects of the lower modes of nature (passion and ignorance) completely vanish. The devotee becomes fully enlightened by virtue of his devotional service, and thus he comes to know the path of the Lord and the way to attain Him. As all doubts diminish, he becomes a pure devotee.

Thus end the Bhaktivedanta Purports to Śrī Īśopaniṣad, the knowledge that brings one nearer to the Supreme Personality of Godhead, Kṛṣṇa.