I realize that this is an old topic, but as I looked through I did not find someone who used a scriptural reference to the law of the gospel. There are several. The law of the gospel is to take care of the poor and the needy. Doctrine and Covenants 104: 17-18 states;
17 For the earth is full, and there is enough and to spare; yea, I prepared all things, and have given unto the children of men to be agents unto themselves.
18 Therefore, if any man shall take of the abundance which I have made, and impart not his portion, according to the law of my gospel, unto the poor and the needy, he shall, with the wicked, lift up his eyes in hell, being in torment.
We know that the full name of the gospel is the gospel of Jesus Christ, (he references that in the above verse) so the term “law of the gospel” can be used synonymously with the “law of Christ,” since it is His gospel. With that in mind, Galatians 6:2 reads;
2 Bear ye one another’s burdens, and so fulfil the law of Christ.
The gospel of Christ in a general sense is the new and everlasting covenant (DC 66:2), but the law of the gospel or the law of Christ are very specific, and we who have been through the temple have covenanted to take care of the poor and the needy through agreeing to obey this law. Hope it helps. Happy studying!