The Mekhilta takes a detour from the Exodus narrative to establish a principle about prayer: the prayers of the righteous are short. Not flowery. Not elaborate. Short.
The proof comes from a story. A certain disciple once led the prayer service before his master and recited the blessings in abbreviated form. The other students mocked him, calling him "the shortening disciple" — a nickname that treated brevity as incompetence. Surely a proper prayer leader should be expansive, eloquent, thorough in his blessings.
The master shut them down with a single example: "He is not shorter than Moses." When Moses' sister Miriam was struck with tzaraat (a skin affliction), Moses prayed for her healing with just five Hebrew words (Numbers 12:13): "El na refa na lah" — "God, I pray You, heal her, I pray You." Five words. The greatest prophet in Israel's history, interceding for his own sister's life, and he used five words.
The midrash (rabbinic interpretive commentary) makes no attempt to explain why short prayers are preferable. It simply establishes the precedent through Moses' example and lets the implication speak for itself. If the man who spoke face-to-face with God saw no need for lengthy supplication, then brevity in prayer is not laziness or disrespect. It is the style of the righteous — direct, urgent, and stripped of everything unnecessary. The "shortening disciple" was not failing at prayer. He was following the example of the greatest prophet who ever lived.