This quote from Fr. Hans is largely a quote from George Bernanos. The full quote is:
“The curve described by a saint’s life is governed by its own mysterious law, which is a ‘free, docile, and pure’ will having nothing in common with the so-called ‘destiny of great men.’ The saint’s destiny is determined by a very different rhythm: ‘The beginnings are slow, often wearisome. The conflicts come from the outside, and they also seem to come from within. Then, once the work has found its mysterious balance, it’s as if it were wrenched from the earth and released to pure flight.’ ”—Fr. Hans Urs von Balthasar, Bernanos: An Ecclesial Existence
The point here is not to become discouraged in the upward path to be a better version of ourselves. The analogy I like to think of is summiting a mountain. The trail can be more challenging at times, and perhaps your same weaknesses hit you time and time again. From a hiking perspective, maybe that’s a bad knee. From a spiritual perspective, maybe that’s the same sin that always comes back to haunt you. It’s completely normal to be pressured in the same areas. The enemy knows your sore spots, and he relentless presses upon them, often coming back stronger than in prior attacks. Jesus warns us of that:
“When the unclean spirit has gone out of a man, he passes through waterless places seeking rest; and finding none he says, ‘I will return to my house from which I came.’ And when he comes he finds it swept and put in order. Then he goes and brings seven other spirits more evil than himself, and they enter and dwell there; and the last state of that man becomes worse than the first.”—Luke 11:24-26 (RSVCE)
It reminds me of my past when I would host house parties and drink way too much. To actually have a change in my life, it wasn’t enough to just sweep up my place and clean it up after a party… my place (and I) would just get trashed again next time with the same partying habits., I needed to reject that way of life and replace that with time spent elsewhere. In times of temptation, it certainly has helped me to pray, and it has helped me to pray specifically for what I ought to do to fill the time, drawing me away from any opportunity to bite that dreaded apple of temptation, down in those moments where my knees feel most weak. When your knees feel weak, you can get on them and pray!