“Rejoice with rejoicing ones, and weep with weeping ones” (Romans 12:15; LITV).
“Rejoice with them that do rejoice, and weep with them that weep” (Romans 12:15; KJV).
“… to rejoice with the rejoicing, and to weep with the weeping” (Romans 12:15; YLT).
True believers weep with other true believers who are weeping; they care for and suffer with the suffering member.
“But God tempered the body together, giving more abundant honor to the [member] having need, that there not be division in the body, but [that] the members might have the same care for one another. And if one member suffers, all the members suffer with [it]. If one member is glorified, all the members rejoice with [it.] And you are Christ’s body, and members in part” (1 Corinthians 12:24-27).
There is significant spiritual oneness in “weeping with” and “suffering with” those part of the SAME BODY OF CHRIST. There are obvious limits, of course:
“For who among men knows the things of a man, except the spirit of a man within him?” (1 Corinthians 2:11)
“The heart knows the bitterness of its soul, and a stranger does not mix in its joy.” (Proverbs 14:10)
There is a sense in which the individual spiritual “members in part” of Christ’s body cannot fully understand or know the anguish of a fellow believer’s soul since we are not that person and/or that precise thing has not happened to us. Nevertheless, Romans 12:15 and 1 Corinthians 12:26 are beautiful passages that God has inspired and presented to us as means of comforting our brothers and sisters in Christ in the midst of their anguish.
Also, it is in NO WAY a paradox or contradiction for painful (and even perpetual) grief to run parallel with constant rejoicing.
“… as grieved, yet always rejoicing; as poor, yet enriching many; as having nothing, yet possessing all things” (2 Corinthians 6:10).
“Even in laughter the heart is sorrowful, and the end of that joy [is] heaviness” (Proverbs 14:13).
Grieving and rejoicing may reside at the same time in different senses in the same regenerate heart. Perhaps the grief is like unto rapidly moving water “above ground,” while the rejoicing is only a slow subterranean trickle. Or, perhaps after some time passes, the rejoicing is now the rapidly flowing water, while the never-ceasing grief in the heart has calmed and descended “under ground” as the slow subterranean trickle (cf. Romans 9:1-2; Philippians 4:4).
May we pray to God the Father through His Son Jesus Christ for God the Holy Spirit’s help and assistance in offering prudent prayers and good, timely, congruous, and seasonable words to comfort and edify our brothers and sisters who may have a heavy heart (Romans 8:26-39).
“A word rightly spoken [is like] apples of gold in settings of silver” (Proverbs 25:11).
“[As] he who takes away a garment in cold weather, [and as] vinegar on soda, [so is] he who sings songs on a heart [in] misery” (Proverbs 25:20; LITV).
“[As] he that taketh away a garment in cold weather, [and as] vinegar upon nitre, so [is] he that singeth songs to an heavy heart” (Proverbs 25:20; KJV).
“Whoso is taking away a garment in a cold day, [Is as] vinegar on nitre, And a singer of songs on a sad heart” (Proverbs 25:20; YLT).
“Heaviness in a man’s heart makes it droop, but a good word makes it glad” (Proverbs 12:25).
Apparently, the insensitive “salt-in-the-wound” incongruity is a particular kind of song sung to a heavy (sad) heart. Presumably a timely Psalm would not be a thoughtless irritant, but a balm of healing.
“Therefore, let us draw near with confidence to the throne of grace, that we may receive mercy, and we may find grace for timely help” (Hebrews 4:16).
“Hope deferred makes the heart sick, but a tree of life [is] desire coming” (Proverbs 13:12).
Our desire is to love, correct, rebuke, and build up those who profess the true gospel, and not to destroy (cf. 2 Corinthians 10:8). Let true believers thoughtfully and deliberately consider one another, to incite and provoke unfeigned love and good works (cf. 2 Corinthians 6:6-18).
“And let us consider one another, to incitement of love and of good works, not forsaking the assembling together of ourselves, as [is the] custom of some, but exhorting, and by so much more as you see the Day drawing near” (Hebrews 10:24-25).