D&C 41 - 42

In the preface to the Doctrine and Covenants, the Lord referred to the Church as the "the only true and living church upon the face of the whole earth" (Doctrine and Covenants Section 1:30) A "living church" would be organic in nature in that it would grow and develop. This becomes evident in the 41st and 42nd sections. Edward Partridge is called to be the first Bishop in the Church and "that he should be appointed by the voice of the church, and ordained a bishop unto the church, to leave his merchandise and to spend all his time in the labors of the church;" (Doctrine and Covenants Section 41:9) But even at that time, the Law and his duties were not yet known in that he was told "see to all things as it shall be appointed unto him in my laws in the day that I shall give them." (Doctrine and Covenants Section 41:10)

The saints were told to "go to the Ohio; and there I will give unto you my law;" (Doctrine and Covenants Section 38:32) In the 42nd section the Lord begins to give that law - "hearken and hear and obey the law which I shall give unto you." (Doctrine and Covenants Section 42:2)

The first commandment of the law that was given to the elders of the Church was to "go forth in my name, every one of you...in the power of my Spirit, preaching my gospel, two by two, in my name, lifting up your voices as with the sound of a trump, declaring my word like unto angels of God.
7 And ye shall go forth baptizing with water, saying: Repent ye, repent ye, for the kingdom of heaven is at hand.
...inasmuch as ye shall find them that will receive you ye shall build up my church in every region—" (Doctrine and Covenants Section 42:4, 6 - 8). And the commandment was given "that they shall go forth for a little season, and it shall be given by the power of the Spirit when they shall return." (Doctrine and Covenants Section 42:5)

My first thought was this commandment was given only to those in Kirtland at that time and that the spirit would tell those bethren when they should return. But the more I study the scriptures, the more I realize that his mind or perspective is higher than ours and his words are for all; that a little season in the Lord's perspective may be a great deal different than our own.

If this commandment was for all, then this little season may be "two years" as is presently "given by the power of the Spirit" for all missionaries. We know that at other times, the Spirit has dictated other times when they should return.

11 Again I say unto you, that it shall not be given to any one to go forth to preach my gospel, or to build up my church, except he be ordained by some one who has authority, and it is known to the church that he has authority and has been regularly ordained by the heads of the church.
(Doctrine and Covenants Section 42:11)

12 And again, the elders, priests and teachers of this church shall teach the principles of my gospel, which are in ...the Book of Mormon, in the which is the fulness of the gospel.
13 And they shall observe the covenants and church articles to do them, and these shall be their teachings, as they shall be directed by the Spirit.
14 And the Spirit shall be given unto you by the prayer of faith; and if ye receive not the Spirit ye shall not teach.
(Doctrine and Covenants Section 42:12 - 14)

I see this as the first commandment or the law for all missionaries.