Levites Sound Trumpets and a Ram's Horn by the Seaby emmanuel_higgins

Psalms 98:5

Sing unto the LORD with the harp; with the harp, and the voice of a psalm.

Sing unto the Lord with the harp joined to the voice of a psalm in melody and song, with joyful singing and musical instruments. The psalms are songs of praise meant not only to be read and studied but to be sung, and together with verse 6 the harp with trumpets and cornet shows that instruments are fitting in worship when properly employed. Instrumental music joined to the voice is rightly used in praise, yet it is not pleasing to God without the right spirit and a good purpose or when heart and life are corrupt, for its effect depends on the hearts of those who perform it. It belongs to a prophetic, joyful song of the Lord's coming to judge the earth with righteousness and equity when all creation rejoices, expressing hope in Christ's second coming and welcoming the coming King and his reign. The singing with harp and new song celebrates his marvelous victory, his righteousness openly shown and his mercy and truth with salvation seen to the ends of the earth, joined with Psalms 96 and 97 in the millennial jubilee when it is said among the heathen that the Lord reigns, a personal coming before the millennium that begins millennial glory.

Worship with Music and Song

The verse commands praise to the Lord with the harp joined to the voice of a psalm, with melody and song, including joyful singing with musical instruments. It sets instrumental music joined to the voice as the proper way to sing praise to the Lord.
The psalms are songs of praise meant not only to be read and studied but also to be sung, and this verse names the harp and the sung psalm as ways to praise the Lord. Together with verse 6 it shows that praising the Lord with harp, the voice of a psalm, trumpets, and cornet is fitting worship, calling for joyful praise with singing and musical instruments. Those verses support the use of instruments in church when they are properly employed.
Instrumental music joined to the voice is properly used in praise, but it is not pleasing to God when used without the right spirit and a good purpose or when the heart and life are corrupt. Its effect depends on the hearts of those who perform it.

Christ's Coming to Judge

The call to sing to the Lord with harp and voice of psalm belongs to a prophetic, joyful song about the Lord's coming to judge the earth with righteousness and equity, as set forth in the following verses when all creation rejoices. It is joyful praise with harp and song in view of his coming and judgment, expressing hope in Christ's second coming. That praise, when his righteousness and justice are openly recognized, points toward the eternal song declaring his righteousness.

Its joyful praise welcomes the coming King and his reign, inviting earth and heaven and all creation to join in joy. The singing with harp and new song celebrates his marvelous victory, his righteousness openly shown to the heathen and recognized with justice, his mercy and truth to Israel, and salvation seen by all the ends of the earth. The verse is closely joined with Psalms 96 and 97 in describing the millennial jubilee and millennial times, when it is said among the heathen that the Lord reigns and heaven, earth, sea, field, trees, floods, and hills rejoice.

The coming and judgment in Psalm 98 is described in language as literal in style as the coming and judgment in Psalm 50, contains distinct allusion to millennial times with millennial matter interwoven into its context, and is personal and pre-millennial, beginning millennial glory and belonging before the millennium, as shown by the whole structure of Psalms 96, 97, and 98 and by Hebrews 1:6. The rejoicing is before the Lord because he comes, solemnly repeated three times, to judge the earth with righteousness and equity. That coming is with clouds and darkness round about him, righteousness and judgment as the habitation of his throne, fire before him burning up enemies, lightnings enlightening the world till the earth trembles, the heavens declaring his righteousness, all people seeing his glory, and hills melting like wax at the presence of the Lord of the whole earth.