Sutra:
158. upAyAntharangaLil nenju sellAmaikkum kAlakshEbaththukkum inimaiyAlE vidavoNNAmaiyAlum nadakkum.

Meaning:
The remembering/repetition of this mantra will happen without break for the following reasons: 1. it will prevent the mind from seeking other means, 2. having this there is no need for another thing to spend the time with, 3. it cannot be let go because of it's great sweetness.

Sri PBA Swami's Sarartha Deepikai:
The recitation of this mantra will prevent one from seeking other means which might happen due to prior bad habits. Its recitation will occupy all the time such that there will not be time left for other things. Its sweetness is so great that its recitation will happen without stop.

For all these reasons also, the present tense was used in saying prapadhye.