Romans 12:15

“Rejoice with them that do rejoice, etc..] Not in anything sinful and criminal, in a thing of nought, in men's own boastings; all such rejoicing is evil, and not to be joined in; but in things good and laudable, as in outward prosperity; and to rejoice with such, is a very difficult task; for unless persons have a near concern in the prosperity of others, they are very apt to envy it, or to murmur and repine, that they are not in equal, or superior circumstances; and also in things spiritual, with such who rejoice in the discoveries of God's love to their souls, in the views of interest in Christ, and of peace, pardon, and righteousness by him, and in hope of the glory of God; when such souls…”

“Rejoice with them that rejoice; and weep--the "and" should probably be omitted. with them that weep--What a beautiful spirit of sympathy with the joys and sorrows of others is here inculcated! But it is only one charming phase of the unselfish character which belongs to all living Christianity. What a world will ours be when this shall become its reigning spirit! Of the two, however, it is more easy to sympathize with another's sorrows than his joys, because in the one case he needs us; in the other not. But just for this reason the latter is the more disinterested, and so the nobler.”

“Rejoice with them ... - This command grows out of the doctrine stated in Romans 12:4-5, that the church is one; that it has one interest; and therefore that there should be common sympathy in its joys and sorrows. Or, enter into the welfare of your fellow-Christians, and show your attachment to them by rejoicing that they are made happy; compare 1 Corinthians 12:26, “And whether .... one member be honored, all the members rejoice with it.” In this way happiness diffuses and multiplies itself. It becomes expanded over the face of the whole society; and the union of the Christian body tends to enlarge the sphere of happiness and to prolong the joy conferred by religion. God has bound the…”

“Rejoice - The direct opposite to weeping is laughter; but this does not so well suit a Christian. Romans 12:16”

“Rejoice: Isa 66:10-14; Luk 1:58, Luk 15:5-10; Act 11:23; Co1 12:26; Co2 2:3; Phi 2:17, Phi 2:18, Phi 2:28 weep: Neh 1:4; Job 2:11; Psa 35:13, Psa 35:14; Jer 9:1; Joh 11:19, Joh 11:33-36; Co2 11:29; Phi 2:26; Heb 13:3 Romans 12:16”