Matt. 5:14 - Jesus says a city set on a hill cannot be hidden, and this is in reference to the Church. The Church is not an invisible, ethereal, atmospheric presence, but a single, visible and universal body through the Eucharist. The Church is an extension of the Incarnation.
Matt. 12:25; Mark 3:25; Luke 11:17 - Jesus says a kingdom divided against itself is laid waste and will not stand. This describes Protestantism and the many thousands of denominations that continue to multiply each year.
Matt. 16:18 - Jesus says, "I will build my 'Church' (not churches)." There is only one Church built upon one Rock with one teaching authority, not many different denominations, built upon various pastoral opinions and suggestions.
Matt. 16:19; 18:18 - Jesus gave the apostles binding and loosing authority. But this authority requires a visible Church because "binding and loosing" are visible acts. The Church cannot be invisible, or it cannot bind and loose.
John 10:16 - Jesus says there must only be one flock and one shepherd. This cannot mean many denominations and many pastors, all teaching different doctrines. Those outside the fold must be brought into the Church.
John 17:11,21,23 - Jesus prays that His followers may be perfectly one as He is one with the Father. Jesus' oneness with the Father is perfect. It can never be less. Thus, the oneness Jesus prays for cannot mean the varied divisions of Christianity that have resulted since the Protestant reformation. There is perfect oneness only in the Catholic Church.
John 17:9-26 - Jesus' prayer, of course, is perfectly effective, as evidenced by the miraculous unity of the Catholic Church during her 2,000 year history.
John 17:21 - Jesus states that the visible unity of the Church would be a sign that He was sent by God. This is an extremely important verse. Jesus tells us that the unity of the Church is what bears witness to Him and the reality of who He is and what He came to do for us. There is only one Church that is universally united, and that is the Catholic Church. Only the unity of the Catholic Church truly bears witness to the reality that Jesus Christ was sent by the Father.
http://www.scripturecatholic.com/the_church.html#the_church-V