There are various levels in prayer and its efficacy. These may depend on the conditions of man on one hand, and the degree of finality to which Divine decisions have advanced on the other.

The change in man, which confers upon him (or upon the subject for whom one prays) the capacity to draw forth and to receive Divine favour, is accomplished by some with little effort, while others may require continuous and most intense prayer. Still others may need to have their prayers accompanied by some devout act or acts indicating true repentance and submission.

Moreover, there is a distinction between states of 'general propensity' (before a decree has been issued), a definite decision (after a decree), and a final and absolute decision (a decree accompanied by an oath).

The first two are states of relative potentiality, in which decrees may be averted and changed. In the words of our sages: "An outcry benefits man both before a decree and after a decree." The third case, however, is - generally speaking - final and irrevocable.

Now we have seen that prayer is subject to the principle that "a stirring from Above is in response to a stirring or initiative from below."

In context of the preceding, we understand also why it is necessary to pray and perform certain acts to have our needs and requests attended to, notwithstanding the fact that G‑d knows these needs beforehand.

Nonetheless, the implications of this idea in general, and particularly in terms of man having the power - especially through prayer - to avert or convert 'bad' (i.e., severe) decrees, remain rather difficult. Even when invoking the principle of "potentiality and actuality," which answers the question of change, we are still left with an equally difficult problem: it would seem that if not G‑d's will, then at least G‑d's knowledge would change as man's condition changes through prayer.

This problem, however, is no more than a restatement of the classical dilemma of yedi'ah-bechirah, the enigma of G‑d's foreknowledge of the contingent (the variables of the possible, subject to man's freedom of choice). "Just as we do not (indeed: cannot) enquire after (the necessary truth of) G‑d's knowledge being unchanged by the fact of there being a category of the contingent, so we cannot enquire after it being unchanged by prayer. Nonetheless, we believe that the category of the contingent is real, seeing that experience testifies to it. Likewise we believe that prayer is effective in nullifying a decree, as experience testifies to it."

If the Divine will were distinct from G‑d Himself (as is the case with man and human will), one could properly speak of a change from 'before' to 'after.' If there were but the faintest similarity between human will and the Divine will - even of the sort of, for example, some analogous relationship between inanimate matter and pure intellect etc. - it might be possible and proper to pose our problem. In fact, however, it is written, "My thoughts are not your thoughts" (Isaiah 55:8).