Servants, like angels, speak by the power of the Holy Ghost, wherefore they speak the words of Christ. The words of Christ tell you all things what ye should do. But when a person is NOT speaking by the power of the Holy Ghost, they are not being servants of God but are rather servants to themselves. Even the prophet does not speak by the power of the Holy Ghost all the time. Not everything the prophet says is inspired. Even when the prophet speaks and he is inspired, it doesn’t apply to everyone in every situation or circumstance, it only applies to those who receive the witness from the Holy Ghost telling them that they received it correctly and that it applies to them. So, Jesus tells us to look for the Holy Ghost’s witness when he speaks and we are also supposed to look for the Holy Ghost’s witness when prophets speak. Be that prophet you, I or the ones at the head of the LDS church. In this way, we are not relying on men, but on God. We are accepting the teachings which are scripture and not the philosophies of men which the scriptures are mingled with.
ONLY when missionaries, teachers, bishops, presidents and apostles speak by the power of the Holy Ghost are they acting as servants of God. And when they do so, we will know for ourselves that they are speaking by the power of the Holy Ghost because we will be moved by the power of the Holy Ghost. This happens often during talks and classes and people learn by the Holy Ghost and not by men. It becomes a personal revelation process rather than an instruction by men.