Just looking back at that verse from the Udana, translated by F.L.Wooward, to put it in a more modern idiom:
With mindfulness of the body present,
restrained in her sixfold sense contact,
the seeker continuously collected
can know nibbāna herself.
I appreciate the poise in this discipline. Here it reminds me of one of my favourite short suttas, called ‘Crossing over the Flood’ (SN 1.1), where the Buddha says he: “…crossed over the flood without pushing forward, without staying in place.”
“When I pushed forward, I was whirled about. When I stayed in place, I sank. And so I crossed over the flood without pushing forward, without staying in place.”
The whole sutta, translated by Thanissaro Bhikkhu can be found at: