Speaking to one another. Literally, this would denote antiphonal singing, but this is rather an artificial idea for so simple times. It seems here to denote one person singing one hymn, then another another, and so on; and the meetings would seem to have been for social Christian enjoyment rather than for the public worship of God.
In the Epistle to the Colossians it is, "Teaching and admonishing one another with psalms," and this has more of the idea of public worship; and if it be proper to express joyful feelings in the comparatively private social gatherings of Christians, it is proper to do the same in united public worship.
In psalms and hymns and spiritual songs. The precise meaning of these terms is not easily seen; "psalms" we should naturally apply to the Old Testament psalms, but the want of the article makes the meaning more general, equivalent to "songs with the character of the psalms;" hymns, songs celebrating the praises of the Divine Being, Father, Son, and Holy Ghost; "spiritual songs" or odes of a more general cast, meditative, historical, hortatory, or didactic.
But these must be "spiritual," such as the Holy Spirit would lead us to use and would use with us for our good. The two clauses correspond: "be filled with the Spirit;" "speaking in spiritual songs."
Receive the Spirit—pour out the Spirit; let your songs be effusions sent forth from your hearts with the aroma of the Holy Spirit. Singing and making melody with your heart to the Lord; i.e. to the Lord Jesus.
Some have argued that while ἄδοντες denotes singing, ψάλλοντες means striking the musical instrument. But ψάλλω is so frequently used in a more general sense, that it can hardly be restricted to this meaning here.
The great thought is that this musical service must not be musical only, but a service of the heart, in rendering which the heart must be in a state of worship.