I read some seventeenth-century Reformed theologians arguing that because baptism is effective it must be more than a seal. I read others arguing (against Socinians) that baptism is effective because it is a seal, not just a sign.
Someone needs to wade through the literature and give us a dissertation on this. As it stands now, I don’t understand how anyone can claim to speak for the whole of Reformed theology and say what it means for the sacraments to be seals.
I can testify to this problem in the 16th and 17th century literature, having waded through more of it than I can to recall. Every one in the Reformed tradition seems to agree that sacraments are seals, but it seems as if every theologian has his own interpretation of what “seal” means. It’s all rather bewildering.