St. Ambrose, speaking of tears, explains David's saying, “Every night wash l my couch with my tears,” and goes on to speak of Christ bearing our griefs and infirmities. Everything should be referred to His honour, and we ought to rejoice with spiritual joy, but not after a worldly fashion.
21. And who can now fail to understand that the holy prophet said for our instruction: “Every night will I wash my couch and water my bed with my tears”? For if you take it literally for his bed, he shows that such abundance of tears should be shed as to wash the bed and water it with tears, the couch of him who is praying, for weeping has to do with the present, rewards with the future, since it is said: “Blessed are you that weep, for you shall laugh;” or if we take the word of the prophet as applied to our bodies, we must wash away the offenses of the body with tears of penitence. For Solomon made himself a bed of wood from Lebanon, its pillars were of silver, its bottom of gold, its back strewn with gems. What is that bed but the fashion of our body? For by gems is set forth the splendour of the brightness of the air, fire is set forth by the gold, water by silver, and earth by wood, of which four elements the human body consists, in which our soul rests, if it do not exist deprived of rest by the roughness of hills or the damp ground, but raised on high, above vices, supported by the wood. For which reason David also says: “The Lord will send him help upon his bed of pain.” For how can that be a bed of pain which cannot feel pain, and which has no feeling? But the body of pain is like the body of that death, of which it is said: “O wretched man that I am, who shall deliver me from the body of this death?”
22. And since I have inserted a clause in which mention is made of the Lord's Body, lest any one should be troubled at reading that the Lord took a body of pain, let him remember that the Lord grieved and wept over the death of Lazarus, and was wounded in His passion, and that from the wound there went forth blood and water, and that He gave up His Spirit. Water for washing, Blood for drink, the Spirit for His rising again. For Christ alone is to us hope, faith, and love— hope in His resurrection, faith in the laver, and love in the sacrament.
23. And as He took a body of pain, so too He turned His bed in His weakness, for He converted it to the benefit of human flesh. For by His Passion weakness was ended, and death by His resurrection. And yet you ought to mourn for the world but to rejoice in the Lord, to be sad for penitence but joyful for grace, though, too, the teacher of the Gentiles by a wholesome precept has bidden to weep with them that weep, and to rejoice with them that do rejoice.
24. But let him who desires to solve the whole difficulty of this question have recourse to the same Apostle. “Whatsoever you do,” says he, “in word or deed, do all in the Name of our Lord Jesus Christ, giving thanks to God the Father by Him.” Let us then refer all our words and deeds to Christ, Who brought life out of death, and created light out of darkness. For as a sick body is at one time cherished by warmth, at another soothed by cool applications, and the variation of remedies, if carried out according to the direction of the physician, is healthful, but if done in opposition to his orders increases the sickness; so whatever is paid to Christ is a remedy, whatever is done by our own will is harmful.
25. There ought then to be the joy of the mind, conscious of right, not excited by unrestrained feasts, or nuptial concerts, for in such modesty is not safe, and temptation may be suspected where excessive dancing accompanies festivities. I desire that the virgins of God should be far from this. For as a certain teacher of this world has said: “No one dances when sober unless he is mad.” Now if, according to the wisdom of this world, either drunkenness or madness is the cause of dancing, what a warning is given to us among the instances mentioned in the Divine Scriptures, where John, the forerunner of Christ, being beheaded at the wish of a dancer, is an instance that the allurements of dancing did more harm than the madness of sacrilegious anger.
Source: Concerning Virgins (New Advent)