The following video covers Ambrosiaster’s view of:
-How baptism is symbolic
-The sacraments are not needed to be saved
Further, we discuss how the Church Fathers often read much differently when we do not read into them Catholic presuppositions.
Note: This article was written before the author’s conversion to Orthodoxy.
Orthodox Christian Theology 
Just a quick comment: In Catholic theology (in Thomas at least), the sacraments effect through signifying. In the most commonplace definition of sacrament, an efficacious sign of grace, it is the word “sign” that stands in the middle of it.
From this I mean to say that there is nothing contrary to Catholic doctrine in any Father speaking about baptism or sacrament as a sign. We should be more worried if they didn’t!
And I must confess that I know almost nothing about Ambrosiaster. A quick search reveals that I am not the only one.
The question is whether some of the Fathers believed in baptismal regeneration in the same sense as the RCC does now. Remove the presuppositions, and we are given a much different view of the significance of baptism.