Ambrose just showing how he defends the heretical belief that No Sacrament At All is necessary for salvation - it's like he needs his fix or something.
Please note that Ambrose, like Fr. Kramer and all other NSAAers, cannot bring themselves to defend any sacrament - and it is particularly impossible for them to defend the necessity of the sacrament of baptism unto salvation as they no not believe they are necessary for anything at all.
Trent's catechism teaches the reason for this is because Ambrose and all NSAAers despise the sacraments.