A Christian does not belong to a club, group or organisation but the Body of Christ. It means that we are part of a community of believers and therefore are expected to lead a way of life that reflects our sense of belonging and responsibility to the community. In other words, no one can be a Christian alone. We are accountable to our leaders and other members. The leaders, on their part, work for the good of the whole community.
Moses was unable to go into the Promised land because God had commanded him not to do so. It was the result of Moses' failure to obey God completely during an incident in the desert. Although it may seem unfair that Moses, of all people, is denied entry into the Promised land after all that he had done as the leader, God holds Moses accountable, and for his part, Moses obeys God.
When Joshua becomes the new leader of the people, the burden of responsibility falls on him, and the people are now accountable to him and are expected to obey him.
Jesus tells the disciples that in their relationship with him and with one another, they should also have a sense of accountability and responsibility. Those who do wrong are to be held accountable by other members of the community who have to help the former realise their errors, repent and change their ways. The community leaders are responsible for judging the actions of those who have done wrong and decide for the good of the whole community.
Lord, help me be responsible and accountable to my community.