katham ayathA bhavanti bhuvi datta-padAni nRNAm
The immediately obvious translation here is that the Rishis place (dadhuH) in You (tvayi) their thoughts, deeds and actions. But both Sridhara and Jiva divide mano-vacana-Acaritam in a different way as, "the actions of the mind" and "the actions of the speech." Sridhara interprets the first to be the tAtparya, or inner sense, and the abhidhA, which in the overall context of the chapter means the direct meaning. In other words, this is about the actions of the Shrutis: the inner meaning applies to You (tvayi), the personal God, as do the meanings of the words themselves.
Now the last line is, according to Sridhara Swami the alankara (rhetorical device) known as nidarshana, to Jiva it is an arthantara-nyasa. There is also the alankara known as drishtanta, or example. The three are quite similar and it is a bit hard to differentiate them. The basic principle of the first two is that a seemingly unrelated topic is brought up that has some parallels with the subject under discussion. It can either act as a counterpoint, stating the contrary to the issue in question, or act in support of it.
Basically all alankaras are comparisons of some kind, though some may be highlighting the similarities (sadRzya-garbha) and some the differences (virodha-garbha).
It is a question:
How (katham) could the feet (padAni) of men (nRNAM) placed on the ground (bhuvi) become (bhavanti) otherwise (ayathA)?Now what does that mean? Well it has to apply to the immediately previously line. So the thoughts and words of the Shrutis which are placed in Krishna are similar to the feet placed on the earth. Sridhar says, "Whether placed on earth, stones, bricks or whatever, they do not go away from the earth itself (i.e., all of these things are transformations of the earth), so similarly, when the Shrutis talk of something that is a transformation (vikAra), they are in fact ultimately establishing You, the cause of all and the Supreme Truth."
Jiva Goswami says,
Here men refers to all those walking on the earth. Whether they are able to see properly or not, how can the footsteps placed on the ground be unsure, i.e., how can they fall anywhere else but on the ground? Of course, they can only end up there. The intent is to say that therefore it does not matter how the Shrutis explain the Ultimate Truth, the end result will always end up in You alone.
So the difference between the two is fairly clear. Jiva Goswami is showing that the ultimate intent and the words of the shastra, even if it is not overtly evident, are always pointing to the Supreme Person.
Let us think about the verse as a whole for a minute. The Brahma-vadi position is that the clay that is the material cause of the universe is the essence of Brahman. The problem is that they for some reason don't take personality into account. Personality or personhood is part of the fact of existence. The other aspects of the Divine Truth--Brahman or Paramatma--do not fully account for personhood.
The example of clay is therefore somewhat misleading as it only seems to refer to an underlying ground of being and not to a supreme conscious being who is the source of our consciousness and personhood and who thus makes love between individuated consciousnesses a possibility, in particular love between the atomic individual and the supreme individual.
Or, put another way, if we accept Bhagavan as the Supreme Truth, then clearly all things must point to Him. Since Brahman is an integral part of Bhagavan, there is no need to "fear" impersonal interpretations. They do not contradict the Bhagavan aspect but are a necessary part of it. And that makes it possible to see the personal truth even when the apparent explanation is impersonal.
This is one of the great arguments about the Upanishads: some statements seem to refer to God as a person, and some seem to refer to God as impersonal. Which ones are more important? The Vaishnava does not deny the impersonal aspect as wrong or exclude it, whereas the Advaitavadi says that the personal God is only a part of the phenomenal universe and thus is only a reflection or a symbol of the Supreme Truth.
But moreover, in the overall context of whether Brahman can be described in words, the answer is that since God is the source of all things--thoughts and words--how can words fail to describe Him? In fact, whether they directly seem to describe Him or not, on a higher level of understanding, they all DO describe Him in some way.
In support, Jiva quotes two verses, which apparently apply to the two interpretation given above:
Both the jnana-yoga that is related to Me and the yoga characterized by devotion free from the gunas, have one purpose, which is indicated by the word Bhagavan. (SB 3.32.32)
Oh the wonder! All the names explain only this Lord. Just as all the flowing rivers heading towards the ocean enter into the ocean, similarly all these names only enter into or describe the Lord. (Shruti cited by Madhvacharya in his Vedanta-bhashya)
So here are the English translations of 10.87.15 as given in some different sources, offered without comment:
The wise recognize this known (seen and heard of) universe to be (no other than) Brahma (Yourself) because it is Brahma alone that remains (when all else is dissolved) and because it is from and into Brahma (the material cause) which remains unchanged, that the universe (its evolute) emanates and returns, even as the earthenware are evolved out of and disappear into clay. Hence (because of its being the material cause of and therefore comprising the entire universe), the Vedic texts have concluded as refering to You whatever is contemplated within the mind (that is, the import of words) and uttered with the tongue (viz., the names). How could the feet of men placed anywhere (on earth) be regarded as not placed on the earth (itself)? (Gita Press)
This perishable world is identified with the Supreme because Brahman is the ultimate foundation of all existence. It remains unchanged though all created things are generated from it and at last dissolved into it, just as clay is unchanged by the products made from it which again merge with it. Thus it is toward You alone that the Vedic sages direct all their thoughts, words, and acts. After all, how can the footsteps of men fail to touch the earth on which they live? (SB 10.87.15) BBT
This world is understood to be great Brahman because it remains unchanged though all created things are generated from it and at last dissolved into it, just as clay is unchanged by the products made from it and which again merge into it. Thus it is toward You alone that the Vedic sages direct all their thoughts, words, and acts. After all, how can the footsteps of men fail to touch the earth on which they live? (SB 10.87.15) Satya Narayan Das.
[They] know this which is perceived to be the Great, by virtue of its being the remainder, for, as with clay, there is [only an] appearance and disappearance of transformations [coming] from the untransformed. As a result, the Rishis have placed the actions of their mind and speech in You. How can the footsteps of men be go elsewhere when they are placed on firm ground?