D&C 75

As the saints continued to be called to the preach the gospel, the Lord again provided more instruction as the bethren were called to serve mission saying -

"Hearken, O ye who have given your names to go forth to proclaim my gospel, and to prune my vineyard.
3 Behold, I say unto you that it is my will that you should go forth and not tarry, neither be idle but labor with your might—
4 Lifting up your voices as with the sound of a trump, proclaiming the truth according to the revelations and commandments which I have given you."  (Doctrine and Covenants | Section 75:2 - 4)

Obviously, this work would cause a great strain on the temporal sustaining of their families.  I'm sure these men wanted to some help to know what they should do.  But before the Lord provided an answer to their inquiries, He somewhat chastises one of the previously called missionaries saying -

"...verily I say unto my servant William E. McLellin, I revoke the commission which I gave unto him to go unto the eastern countries;
7 And I give unto him a new commission and a new commandment, in the which I, the Lord, chasten him for the murmurings of his heart;
8 And he sinned; nevertheless, I forgive him and say unto him again, Go ye into the south countries."
(Doctrine and Covenants | Section 75:6 - 8)

What touched me were the words "murmuring of his heart".  I wonder how often He would say the same to me.  This is probably the greatest challenge in our lives is to love the Lord with all our hearts.  But even in this chastisement, the Lord provides an opportunity to change and to serve.  Returning to the inquiry of those called on missions, the Lord instructs -

"...O ye elders of my church, who have given your names that you might know his will concerning you—
24 Behold, I say unto you, that it is the duty of the church to assist in supporting the families of those, and also to support the families of those who are called and must needs be sent unto the world to proclaim the gospel unto the world.
25 Wherefore, I, the Lord, give unto you this commandment, that ye obtain places for your families, inasmuch as your brethren are willing to open their hearts.
26 And let all such as can obtain places for their families, and support of the church for them, not fail to go into the world, whether to the east or to the west, or to the north, or to the south."  (Doctrine and Covenants | Section 75:23 - 26)

It was of great importance that these brethren look first after their families and sustanance with an obligation of the members to take care of their families where possible.  But if these called missionaries were unable to obtain support as needed for their families -

"...verily I say unto you, that every man who is obliged to provide for his own family, let him provide, and he shall in nowise lose his crown; and let him labor in the church.
29 Let every man be diligent in all things. And the idler shall not have place in the church, except he repent and mend his ways."  (Doctrine and Covenants | Section 75:28 - 29)

Which suggest to me that we must do everything we can to serve the Lord, but our first priority is the support and care for our families.