Taken from Al-Fawaa’id; translated by Abu Rumaysah
In this lies a great secret from the secrets of Tawheed. This is that the heart cannot become firm, it cannot find satisfaction and it cannot find tranquillity except by reaching out to Him. Everything that is loved and desired besides Him then it must be desired for other than His sake. The One Who is desired, the One Who is beloved in and of Himself, with Whom all matters find their final goal is only one. It is impossible that the final goal be to two destinations just as it is impossible that the beginning of the creation be from two sources.
So the one whose love, desire, will and obedience ends at other than Him then it will be rendered null and void, it will disappear and split off from him no matter how great his need be of it. However the one whose love, desire, will, obedience, awe and reverential fear ends at Him, far removed is He from imperfection, will find himself winning His favours, bliss and rapture, magnificence and splendour, and felicity for eternity.
The servant continuously finds himself altering between the laws of commandments and the laws of decree. Therefore he is perpetually in need of aid to fulfil the commandments and in need of kindness and leniency at the onset of the calamity. It is the extent to which he establishes the obligations that determine how much kindness the servant will receive at the onset of the calamity. Therefore if he completes his obligations both inwardly and outwardly then he will attain kindness and leniency both inwardly and outwardly. If, however, he merely establishes the outward form [of the commandments] without establishing their reality [inwardly] then he will receive an outward kindness and his portion of inward kindness will [greatly] diminish.
So if it is asked: what is this inward kindness?
[I say in reply:] It is what the heart attains of tranquillity and satisfaction at the onset of the calamity and the removal of unrest, confusion and despair. Therefore the servant surrenders and submits himself before his Lord and Master and he emerges in a state of complete rest and tranquillity - looking on at Him with his heart, and his soul at peace. His witnessing His Kindness has distracted him from the severity of the situation. His knowledge of Allah’s excellent choice and decision for him diverts him from feeling the calamity just as does his knowledge that he is nothing but a mere servant upon whom the decrees of his Master take effect, and he can either be pleased with them or angry with them. So if he is pleased then he will attain Pleasure and if he is displeased then his portion is nothing save Displeasure. Therefore this inward kindness is the fruit of this inward action [of being pleased with the decree of Allah], it increases with its increase and decreases with its decrease.
source: mission islam