Baptism and Holy Communion are almost universally observed among Christians and given great importance. That Christ instituted them is almost beyond question, although there were similar--similar--ceremonies in the religions that came before Christianity.
So what of the other ones that are believed by some churches to be sacraments but not seen as such by all? What if we take them individually?
Penance AKA Reconciliation, most often called Confession.
Luther considered the possibility that this was a sacrament because repentance, confessing ones sins and receiving absolution is ancient, Scriptural, and beneficial. But can we say that Christ instituted it, that it involves some physical act or ritual in the way that Baptism and Communion do, or even that there are any physical properties to it? Well, no. Not unless your thoughts and wagging your tongue qualify. That doesn't seem parallel to the water in Baptism or the bread in Communion.
And that is not to say that repentance, confessing ones sins, and asking God for forgiveness have no place in churches which do not consider this to be a sacrament of the Gospel. As said before, it is one of the sacraments in the various Catholic (RC, EO, Old Cath, Coptic, etc.) churches; but there are hardly any reformed churches which consider it to be a sacrament (for the above reasons).
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