Apostolicity

The Church's third mark, Apostolicity, perhaps has one of the closest possible links to Christ. Why? It was instituted by Christ himself. Christ instituted Apostolicity via his creating the authority of the Apostles. This means all bishops, as they are the successors of Apostles, have the authority to exercise the full range of Christ's authority. This means the Church always has Christ with them.
A second way the Church is apostolic is through its tradition. The Apostles pass down the Deposit of Faith through their successors. The Deposit of Faith is the one truth given by Christ that can never be changed. What is eternally true then is eternally true now. This is passed through the Apostles, as they are effectively the messengers of Christ.
A third way the Church is Apostolic is the way she defines doctrine. The rules and philosophy of Christ stay the same, but bishops are able to use his authority to define them for each time. Further, these successors of the Apostles are given the authority to be infallible when ex cathedra, and guided by Christ himself. Furthermore, this means that Christ's authority is constantly with the Church. The Church is not merely founded by Christ but is constantly guided by him. This makes the essence of the Church infallible.
Lastly, tradition is passed through Apostolicity. When the Gospels were written, they were a few decades behind Christ himself. This brings into question how they could be accurate. Before written Scripture was created, there was still Sacred Tradition. This means the Apostles passed down Christ's teachings via Apostolic Tradition.