What is hal in Sufism, and can it be learnt from books?

In Tasawwuf, hal means the state. The knowledge of Tasawwuf has to be imparted from a living shaykh, and the connection with that shaykh is called tálluq; through it the shaykh ensures not only the transfer of knowledge but also the transfer of the state.

As a true teacher, the shaykh helps to eliminate the blameworthy traits and helps the seeker attain the hal of perpetual remembrance. Often, people who learnt merely through books have the information but lack the state, the hal, which comes with tálluq. They may carry the burden of blameworthy traits such as pride or riya, which only tazkiya through connection with a true shaykh could eliminate.

It was Mowlana Rumi's rahimahullah meeting with the dervish Shams-e Tabrizi rahimahullah that completely transformed his life, from an accomplished teacher and jurist to an ascetic. Rumi requested Shaykh Shams-e Tabrizi rahimahullah to take him as a disciple, and it was after that tálluq that Rumi wrote the famous Mathnavi.

For the true state, the hal, to be acquired, one needs to have been in connection, tálluq, with a living teacher for a prolonged period of time; it cannot be achieved in a sitting.

The state of the teacher affects the seeker in either way. If the teacher knows the taste of the Divine Love, he would be able to take the seeker through the journey of Tasawwuf; otherwise, if the teacher has not trudged that path himself, his state of the heart would affect the seeker and they would both remain lost.