In many things in our lives we make oaths or agreements in order to have authority or employment. Medical doctors take an oath to be doctors. In my employment as a software developer I sign non disclosure agreements and security agreements in order to be employed.
While these examples could be argued are devises of men, I believe that God gives us many things in life that operate on similar principles as the things of God, in order that we, as men, might understand the things of God more easily.
When we participate in ordinances and make covenants we are doing similar things to have privileges and authority.
Doctrine and Covenants 90:24
24Search adiligently, bpray always, and be believing, and call things shall work together for your good, if ye walk uprightly and remember the dcovenant wherewith ye have covenanted one with another.
Mosiah 18:8-10
8 And it came to pass that he said unto them: Behold, here are the waters of Mormon (for thus were they called) and now, as ye are desirous to come into the fold of God, and to be called his people, and are willing to bear one another’s burdens, that they may be light;
9 Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life—
10 Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you?
8 And it came to pass that he said unto them: Behold, here are the waters of Mormon (for thus were they called) and now, as ye are desirous to come into the fold of God, and to be called his people, and are willing to bear one another’s burdens, that they may be light;
9 Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life—
10 Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you?