vows help one initiate the relevant Yin Yuan (karma) to help us
realise our goals in the future
but the problem with commoners like us is that our thoughts are
constantly changing and varies countlessly, the second after we
vow, we may not feel as "true" to the moment as before (a crude
analogy will be how you feel before and after you do your
partner)
thus vows need to be practised day-in-day-out, so that it actually
"seeps" into your 8th consciousness, then slowly all your actions
and decisions will start to align behind these vows, thereby
attaining them in due time
side note: because your actions and decisions start to align, you
actually are changing your original karma (bad reference but easy
to understand), this is also how certain people are able to
single-handedly turn their life around