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Collect: O God who alone causes grace in us, refresh anew in us that grace wherein we were brought into union with thee, through Christ our Lord. Amen.
SUMMARY
In the Sed Contra, St. Thomas gives a relatively simple dogmatic argument.
In the Respondeo, we must first distinguish the proper reference of the question. For, it is not speaking of instrumental causality (Christ’s humanity and the sacraments are instrumental causes), rather, it is speaking of principle efficient causality.
Further, it is directly referring to habitual grace, although, indirectly, it refers to actual grace also.
The argument of St. Thomas is relatively simple. His major premise is that “less cannot produce more,” i.e., an effect must be produced by a proportional cause. If we observed a great building, we would not assume the cause of the building is a toddler with a toy hammer, for, a great building needs great causes.