7.21

यो यो यां यां तनुं भक्तः श्रद्धयार्चितुमिच्छति ।
तस्य तस्याचलां श्रद्धां तामेव विदधाम्यहम् ॥

yo yo yāṃ yāṃ tanuṃ bhaktaḥ śraddhayārcitum icchati
tasya tasyācalāṃ śraddhāṃ tām eva vidadhāmy aham

Kṛṣṇa (कृष्ण) is speaking, to Arjuna (अर्जुन).

The verse

Whichever form a devotee wants to worship with faith, I make that very person's faith unshaking.

नेपालीमा

भक्त जुन रूपलाई श्रद्धाले पुज्न चाहन्छ, त्यसै व्यक्तिको श्रद्धा म अडिग बनाउँछु।

Where it sits

7.20 looked like a departure, people going to other gods because desire had taken their knowledge. This verse says he is not absent from that worship. The faith they bring, he is the one who makes firm. 7.22 will say he is also the one who arranged the desires they get back.

Split: यः + यः + याम् + याम् + तनुम् + भक्तः + श्रद्धया + अर्चितुम् + इच्छति + तस्य + तस्य + अचलाम् + श्रद्धाम् + ताम् + एव + विदधामि + अहम्

yaḥ + yaḥ + yām + yām + tanum + bhaktaḥ + śraddhayā + arcitum + icchati + tasya + tasya + acalām + śraddhām + tām + eva + vidadhāmi + aham

Sanskrit, in depth

The words

देवनागरीWordGrammarSense
यःyaḥnominative singularwho.
यःyaḥnominative singularwho. Doubled: whichever person.
याम्yāmaccusative femininewhich.
याम्yāmaccusative femininewhich. Doubled: whichever.
तनुम्tanumaccusative of tanu (तनु)form, body. Here a divine form.
भक्तःbhaktaḥnominative singulara devotee. One who has turned to a form.
श्रद्धयाśraddhayāinstrumentalwith faith.
अर्चितुम्arcituminfinitive of arc (अर्च्)to worship.
इच्छतिicchatipresent, 3rd singularwants. From iṣ (इष्).
तस्यtasyagenitive singularof him.
तस्यtasyagenitive singularof that very one. Doubled, answering yaḥ yaḥ (यः यः).
अचलाम्acalāmaccusative feminineunshaking. Agrees with śraddhām (श्रद्धाम्).
श्रद्धाम्śraddhāmaccusativefaith.
ताम्tāmaccusative femininethat. The faith just named.
एवevaindeclinablethat very.
विदधामिvidadhāmipresent, 1st singularI place, I set. From vi-dhā (वि-धा).
अहम्ahamnominativeI.

The phrases

यः यः याम् याम् तनुम् भक्तः श्रद्धया अर्चितुम् इच्छति yaḥ yaḥ yām yām tanum bhaktaḥ śraddhayā arcitum icchati is whichever devotee, whichever form, wanting to worship it with faith. The doubling is distributive. It covers the other deities of 7.20 one by one, without naming them.

तस्य तस्य अचलाम् श्रद्धाम् ताम् एव विदधामि अहम् tasya tasya acalām śraddhām tām eva vidadhāmi aham is what he does with that faith. He makes it unshaking. He does not say he refuses the worship. He steadies the faith the person already has.

Sanskrit in this line

The doubling is the grammar. yaḥ yaḥ (यः यः) is "whichever person," yām yām (याम् याम्) is "whichever form," and tasya tasya (तस्य तस्य) answers the first pair: "of that very person." One relative, one correlative, each said twice so it travels down the list of forms.

yaḥ (यः) before y (य्) is recited yo (यो). aḥ (अः) before a voiced consonant becomes o (ओ). Both of them: yo yo (यो यो). The visarga is not in the recited line, and both words are still yaḥ (यः).

विदधामि + अहम् vidadhāmi + aham is vidadhāmy aham (विदधाम्यहम्). इ + अ i + a becomes ya (य). The aham (अहम्) at the end is the subject of "I set." Do not leave it inside the verb.

Say it back

Whichever form, then what he does to the faith. If acalām (अचलाम्) becomes "a little faith," stay here. He makes it unshaking.