First: Lengthening the supplication indicates the supplicant’s love, for when a person loves something, he loves to prolong his intimate converse concerning it. In supplication, you are in communion with Allah; thus, making your supplication lengthy and expansive is evidence of your love of conversing intimately with Allah, Glorified and Exalted is He.
Second: Lengthening it allows for details that demonstrate the intensity of a person’s need for his Lord in every circumstance.
Third: It is more conducive to the heart’s presence.
Fourth: It increases one’s reward and worship of Allah, Most High, for supplication is an act of worship for which a person is rewarded.
Fifth: It is a form of persistent entreaty in supplication, and Allah loves those who persist in supplication.
Sixth: By lengthening the supplication, one may mention something that one had forgotten to include in it.
Consider this in the Prophet’s saying, may Allah’s peace and blessings be upon him: “O Allah, forgive me all my sins: their minor and major ones, their secret and open ones, their first and last ones” (1); “O Allah, forgive me what I have sent forth and what I have delayed, what I have concealed and what I have made public, and that of which You have greater knowledge than I” (2); and “O Allah, forgive me my seriousness and my jesting, my mistakes and my deliberate acts; all of that is found in me” (3). These supplications contain details as well as comprehensive expressions, but their benefit is what I indicated earlier.
If it were said: The funeral prayer is founded upon brevity; this is why the opening supplication is not recited in it. So how can we make the supplication expansive and lengthy?
The answer is that supplication is the essence of the prayer, and so it should be made expansive