In the information which it typed below, it talks about "the church". It could mean "churches" in general; or "my church; your church" in particular:

"The Joy of Harmonious Relationships"

Psalms 133:1 (LB): How wonderful it is, how pleasant, when brothers (& sisters!) live in harmony!

Taken from my Bible Commentary: David (writer of this Psalm) stated that harmony is pleasant, precious, and refreshing. Unfortunately, harmony does not abound in the church as it should. People disagree and cause division over unimportant issues. Some seem to delight in causing tension by discrediting others. Harmony is important because:

it makes us a positive example to the world and helps draw others to us;

it helps us function as a body of believers as God meant us to, giving us a foretaste of heaven;

it is renewing and revitalizing because there is less tension to sap our energy.

Living in harmony does not mean we will agree on everything; there will be many opinions just as there are many notes in a harmonious chord of music. But we agree on our purpose in life – to work together for God. Our outward expression of unity should reveal our inward unity of purpose.