Spiritually a plea has the same meaning as prayer. It also suggests applying to arbitrators of spiritual law such as priests and holy men.
Psychological / emotional perspective: When we find ourselves pleading for something – begging or appealing – we have some extreme need for whatever is represented. This might, for instance, be some kind of assistance or sanctuary.
Material aspects: A strongly held feeling or principle will deepen to a plea in dreams, particularly if we feel we are not understood.