"The LORD is the witness between you and the wife of your youth. You have been unfaithful to her. . . ." — Malachi 2:14
Sacrifice is measured by difficulty. Jesus tells us in Luke 21:1-4 that the widow who gave two small coins sacrificed more than all the others did, because she gave all she had.
In Malachi's day not only were people skimping on their temple sacrifices (Malachi 1:7); they couldn't even sacrifice their desires in order to take care of their wives and children. It would have been one thing in God's eyes for men to skimp on what God deserved in order to take care of their families. But the men were also actually being unfaithful to their families.
It is an amazing display of the loving faithfulness of God that he tells the men of Israel that he won't accept their sacrifices if they don't take care of their families. Far too many of God's people have gotten it backwards, neglecting their marriage and family for the sake of their career or even the church. One of my seminary professors once said that God will often ask our families to make sacrifices, but God will never ask us to sacrifice our families.
That statement lines up with this verse. When we are unfaithful to the physical, emotional, and spiritual needs of our families, we are living outside of God's will. And there's never an excuse for that.