"Amazing Grace" was written by the Anglican John Newton in response to his conversion of grace from his life as a slave trader. These lyrics express his moment of conversion:
How precious did that grace appear / the hour I first believed.
This can be reconciled with Catholic teaching because the grace of conversion can indeed be given at certain hours, causing a person to repent of a previously sinful life. However, the lyrics can be problematic because they also can be understood in a manner that makes receiving grace dependent
upon belief. Catholics believe that supernatural grace can be received even by those incapable of belief, such as infants at baptism. Unless a Catholic understands how the lyrics can be reconciled to Catholicism, the lyrics can be ambiguous and confusing.