Nehemiah setup a system of help in case of attack. To repulse the attack would need concerted effort and therefore a trumpet was to be blown at the point where the enemy tried to break through the walls.
We may apply this to the local church. Our battle is spiritual and the weapons of our warfare are not carnal but spiritual. Our attacks from Satan and we need each other to help in fighting against him. This help takes the form of mutual prayer for one another. We hear of a believer who is in trouble and we pray in our church Prayer Meeting and privately for such a one. Some have fallen to temptation and they ask for prayer that they may not fall again. The trumpet is sound to ask for help and the Lord is appealed to directly. In the defence of Jerusalem Nehemiah pointed to the fact that God was with them and would fight for them. Even in their taking up of physical arms they looked to the Lord for help. How much more should we go to the Lord when the attack comes in the form of doctrinal error and confusion that destabilises the spiritually young and inexperienced as well as personal temptation.
We ask for prayer in our prayer meeting in general terms, without going into the specifics of the temptations we face. We ask for prayer for holiness for the whole church and for protection against the power and deceitfulness of sin. We pray for those who are going through deep trials of sickness or calamity of some sort, because we know that Satan often attacks at such a time when we are already under strain. The local church rallies to the defence of one member because every member of the body is precious and is needed for the functioning of the whole body.