The Most Superior Worship

Hadrat [1] Imam-i Rabbani says in the 20th letter of the second volume of his Maktubat:

   O My Dear Brother! This world is the place for work. The next world is the place for getting wages. Strive to do pious actions! The most useful of these actions, the most superior worship is to perform salat. Salat is the archstone of the din (religion). It is the mi'raj [2] for Believers. Then, one should do one's best to perform it well. One should observe its precepts, its conditions, its sunnats [3] and adabs [4] in a manner liked and suitable. When performing salat, one should be careful about its tumaninat [keeping all one's limbs motionless in ruku (bowing during salat), in sajda (prostration), in qawma (standing for a while after straightening up from the bowing position), in jalsa (sitting for a while between the two sajdas), and about the ta'dil-i-arkan (to remain motionless for a while after becoming calm at these four places)]. Many people, paying no attention to these, have been ruining their prayers of salat. They have been neglecting the tumaninat and the ta'dil-i arkan. It was informed that they will be tormented. When salat is performed correctly the hope of salvation will increase. For, the archstone of the din will then have been erected.

[1] Hadrat: title of respect used before the names of great people like and Islamic scholars.
[2] Mi'raj: i) the Prophet's ascension from Jerusalem to heaven. ii)Prophet's Ascension from Jerusalem to the skies.
[3] sunnat: i) (when used alone) The Shari'at; ii) (when used together with the name Book) The hadith of the Prophet. iii) (when used together with the word Fard) Any action, word or thought liked and commanded by the Prophet.
[4] adab: there is a special adab in doing everything. The adab of doing something means to follow the conditions necessary for doing it in the best way.