The marks of the Church are four essential, indivisible characteristics of the Church (cf. DS 2888), possessed by virtue of her having been founded by Christ and her divine mission; they are enumerated in the Nicene Creed.
"This is the one Church of Christ which in the Creed is professed as one, holy, catholic and apostolic" (LG 8). (Cf. CCC 811-812)
-The Daidache Bible
The Church is One because she was founded by Christ. Saint Paul described the Church as the Mystical Body of Christ, made up of diverse members, bonded in charity (cf. 1 Corinthians 12:27). In her intrinsic unity, she is thus an image of the Blessed Trinity, which is her very source. She also possesses visible signs of her unity: the one faith received from the Apostles; the Sacraments; and the bishops, who are the direct successors of the Apostles. (Cf. CCC813-815)
The Church is Holy because she is sanctified by Christ, who is the "Holy One of God"(Mark 1:24; Luke 4:34; John6:69; cf. 1 John 2:20; Acts of the Apostles 2:27; 13:35) and loves her as his Bride; she in turn is empowered to sanctify people by the power of Christ and his Holy Spirit working through her, especially in her Sacraments. (Cf. CCC 823-829)
The Church is Catholic for two reasons: First, she is the one true Church founded by Christ and is intended for everybody throughout the world in every age; second, she in turn is commissioned with preaching the Gospel to all peoples, drawing every human person to the Church for the sake of his or her salvation. Everyone is called to become part of the one Church in Christ. (Cf. CCC 830-856)