That is actually what the word "Catholic" means: the many are one: living as one: working together because thinking together: one heart because one in mind.
His Holiness Pope Francis explains this fundamental truth of human existence and central tenant of true religion in the heart of his new encyclical (together with Pope Emeritus Benedict) Lumen Fidei. Below is my brief summary of the relevant text (#47-48).
Our present world which is so much united materially and technologically is still very much divided regarding truth because there can be no authentic unity in truth without unity in God. The secret to unity is unity of faith. And unity of faith comes first of all from the unicity of God: to know and to confess the one God, living and true. (Fides una est in primis ob unitatem Dei, quem novimus et confitemur. Omnes fidei articuli respiciunt Eum...) We have to apply ourselves to God.
Because the faith is one, the faith must be professed in all of its purity and integrity. (Cum fides una sit, profitenda est in omni puritate et integritate. 48)
For authentic human unity, unity of living faith is essential; i.e. unity in the one true faith of the love of God, manifested in Christ, alive and perpetuated through His Church.