Many spiritual writers say the same thing. The only thing that keeps us from being saints in the formal sense is our lack of will. God provides everything we need. It is our refusal on even the smallest of scale that keeps us from being "saintly".
Regards
Thomas Merton assigns that to our vestigial pride. Unless we humble ourselves completely, we cannot achieve sainthood. Any vestige of pride and arrogance is enough.
One of our parishoners once observed that the priest in question was "a good man" but she said "when I look at him I see [priest's first name]." In other words, his personality was too strong still for us to see an icon of Christ in him. He simply drew too much attention to himself.