It is important for us to develop and then maintain our inspiration to serve the Lord. It helps if we understand first why we are obliged to perform devotional service at all. If we have forgotten why we are making a particular offering, we will not be able to maintain our inspiration, but will gradually begin to think, "I have vowed to perform this activity, but I would really rather be doing something else." This mentality is called niyamagraha, or following the rules and regulations without being aware of the purpose behind them.
Lectures from a Disciple, Vol. 2, Purpose of Sadhana-bhakti