When a devotee of the Lord makes a promise

This quote interests me because devotees of the Lord not only make promises to help others (as is the case here) but also makes personal promises of spiritual practices they will perform. In my experience, there are many times when devotees struggle to keep, or even fail to keep, their promises. But here, Srila Prabhupada notes that the Lord personally arranges to help his devotee keep those promises. Perhaps when we struggle or fail, our difficulty is due not so much to a weakness of our attraction to the mundane, but to a lack of faith in, and dependence on, the Lord. Another point is that the king in this quote knew his own power. We are advised to only promise what is genuinely within our power. If we limit our promises to what we can actually do, and we depend on the Lord, then fidelity to our promises should be totally within the realm of expectation. Here is the quote:

“The assurances and challenges made by Mahārāja Parīkṣit are never exaggerations of his real power. The Mahārāja said that even the denizens of heaven could not escape his stringent government if they were violators of religious principles. He was not falsely proud, for a devotee of the Lord is equally as powerful as the Lord or sometimes more powerful by His grace, and any promise made by a devotee, though it may be ordinarily very difficult to fulfill, is properly executed by the grace of the Lord.”
Purport SB 1.17.17