What is the meaning of niyyah (intention), and is there a way to acquire it, and is its place in the heart, and must it be preserved through acts of obedience?

Linguistically, niyyah (intention) is resolve. Legally, it is the heart's inclination towards what it perceives as conducive to gaining benefit or repelling harm. The place of the niyyah is the heart, by agreement of the imams, and it does not require verbal articulation.

Intention is a condition for the validity of acts of worship. Its purpose is to distinguish acts of worship from habits, and to distinguish some acts of worship from others; this is what jurists focus on. Its purpose is also to distinguish the Worshipped One, which is sincerity, meaning desiring the Countenance of Allah through the worship; this is what the masters of spiritual conduct and theologians concerned with creeds focus on.