Daniel Amen once explained that the solution to generating motivation for investing in spiritual practices lies in finding 'The Picture'. What picture? The picture of a loved one. And to dedicate one's own spiritual practice to the welfare of that loved one.
Basically, the idea is that by investing time and effort in spiritual pursuits, we become mentally healthier because we reduce negativities in our mind and experience a more positive state of mind. Also, we spread to others whatever we are! For example, somebody in a negative state of mind spreads negativity to others. Somebody in a positive state of mind spreads positivity to others! So out of compassion for our loved one(s) in The Picture, we find motivation to continually invest in spiritual practices.