Commentaries:
Robertson's Word Pictures (NT)
Shod with sandals (upodedemenouv sandalia). Perfect passive participle in the accusative case as if with the infinitive poreuesqai or poreuqhnai, (to go). Note the aorist infinitive middle, endusasqai (text of Westcott and Hort), but endushsqe (aorist middle subjunctive) in the margin. Change from indirect to direct discourse common enough, not necessarily due to "disjointed notes on which the Evangelist depended" (Swete). Matthew 10:10 has "nor shoes" (mhde upodhmata), possibly preserving the distinction between "shoes" and "sandals" (worn by women in Greece and by men in the east, especially in travelling). But here again extra shoes may be the prohibition. See on Matthew 10:10 for this.
Two coats (duo xitwnav). Two was a sign of comparative wealth (Swete). The mention of "two" here in all three Gospels probably helps us to understand that the same thing applies to shoes and staff. "In general, these directions are against luxury in equipment, and also against their providing themselves with what they could procure from the hospitality of others" (Gould).
Other Robertson's Word Pictures (NT) entries containing Mark 6:9:
Matthew 10:10
Luke 22:36
Acts 12:8
Ephesians 6:15
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