The piano has a multiple function in worship. It gives pitch, harmonic structure, and rhythm to songs. It is considered a lead instrument and essential to the basic strength of a song. Along with the other pitched instruments, it assists in making key changes.
The guitar can do much the same as the piano. As a lead instrument (often used by a worship leader), it sets pitch, harmonic structure, and rhythm to songs. As a supportive instrument, it brings colour to the song. Along with the other instruments, it introduces songs and makes it possible to medley songs together.
The bass sets and maintains the tempo of the song. Along with the kick (bass drum), it keeps singing consistent. It also gives definition to the chord structure of a song. Even though the guitar and the piano have a bass part to them, it is only the bass guitar that gives an auditory foundation to music. The sound system equalizes the instruments for their function so the bass is designed to anchor the chord of the music.
The synth. is a supportive instrument that brings multiple colours to a song. As the guitar may bring colour to a song as a supportive instrument, the synth. can do much more. It can be many instruments. It gives smooth support as a string section for a slower song. It gives a bold support as a brass section for a faster song. It adds to the song as a flute or most other instruments would do. The synth., along with the piano and guitar, will support vocal (non singing) expressions of worship or the prophetic song.
The drums, as stated before, keep the tempo of the song consistent. Along with the lead instrument, it sets the rhythm pattern for the song. All parts to the drums have distinct functions. We have already spoken about the purpose of the bass drum. The cymbals are like punctuation marks. The toms lead from one point of the song to another by fills. The snare, the bass drum and the hi-hat interact to keep the tempo consistent.
Each instrument used in worship plays an integral part in the corporate expression of worship. In small groups some of these instruments may not be required. But for worship services, without each instrument, there would be holes that can weaken the strength of the worship team to lead.