Probably the calling and sending out of the Seventy was a temporary commission, unlike that of the Apostles, who held their offices permanently. I say temporary, because there seems to be an element of judgment attached to their mission. Jesus points to a “day” when those who heard them would have to answer for how seriously the audience of the Seventy took their words (cf. Luke 10:12).
In Luke 10:5-6 we are told that Jesus sent the Seventy out on a mission of peace. That is, if we take into consideration Jesus warning in Luke 10:3 that they would be among wolves (i.e. rebellious people), he was giving everyone an opportunity to reconsider their ways and repent. The disciples were not to bring down judgment upon anyone who opposed them (cf. Luke 9:52-56). Rather, they were on a mission, which sought to allow Jesus entry into the lives of others. If folks refused him entry, they would still have the opportunity to repent later. Nevertheless, just as the harvest season has a deadline, so, too, was the opportunity to receive Jesus’ peace offering.
Jesus told the Seventy that in the event their message was rejected and they weren’t received in a particular city, they were to shake off the dust from their clothing as a testimony against that city (Luke 10:10-11; cf. 9:5; Acts 13:50-51). Centuries earlier, Nehemiah shook his clothing to say to the people that anyone who didn’t promise to do as he commanded, that one would be like the dust in his lap as far as participation in the promises of God was concerned. In other words, the rebels would be rejected by God (Nehemiah 5:13). Consider the testimony of Livy, an ancient Roman historian:
Then the Roman, gathering up his toga into a fold, said, “We bring you here both war and peace; choose which you will!” When he had said these words, they cried out with no less truculence that he might give them whichever he liked; and on his shaking out the fold again, and announcing that he gave them war, they all replied that they accepted it, and in that same spirit in which they accepted it were resolved to wage it. – [Livy, The History of Rome; Book 21, chapter 18].
When Jesus said the Kingdom of God has come near you (Luke 10:9, 11), he was pointing to Moses’ address to the people concerning the word of God, which Moses declared to the people, before they entered the Promised Land (Deuteronomy 30:11-14). In other words, Jesus claimed the Gospel wasn’t hidden or afar off. That is, it wasn’t so heavenly that one from heaven needed to appear to us and interpret it for us (cf. Daniel 7:15-16), nor is the Gospel beyond the sea that we should require one to go and fetch it for us that we may hear and do it. Rather the Gospel is near to us (Luke 10:9, 11), even in our mouths and in our hearts that we may do it
Jesus claimed the Gospel was something anyone could understand. It’s not all that complicated. It needed neither a heavenly interpreter nor earthly wisdom to understand and do it. The ancient western philosophers used to travel east, over the sea, in order to be taught the secrets of eastern wisdom. After spending years there they would return and interpret life to their disciples. It wasn’t that way with the Kingdom of God. Paul changed this metaphor (cf. Romans 10:6-8) interpreting the sea as death, and indicating one didn’t need to raise Christ from the dead a second time in order to receive the Kingdom of God. Rather, the Gospel of the Kingdom hung on faith or trust in Jesus. The idea is very simple. If one simply confessed Jesus as Messiah and believed God raised him from the dead one would be saved (Romans 10:9-10), or in terms during Jesus public ministry: if one embraced Jesus as Messiah and believed God sent him from heaven, one would be saved. Salvation hung on faith, not sight. It isn’t complicated. One either believed or he didn’t.
Jesus, through the Seventy, set before the people “life and death” (cf. Deuteronomy 30:19). They were expected to choose life. It certainly was in their ability to do so, but, if it wasn’t in their hearts to do so, it would be more tolerable for the ancient gentile cities God judged in the past than for the city that refused the Gospel in Jesus’ day (Luke 10: 12-16; cf. Acts 13:26, 40, 46).