The bell towers are dedicated to the twelve apostles.
THE EPISCOPAL SYMBOLS
The bell tower pinnacles are dedicated to the bishops, who hold the highest rank within the Sacred Ministry as successors to the apostles. The pinnacles are made up of episcopal insignia: the ring, the staff, the mitre, and the cross. The shape of the pinnacles is the staff; the top is the mitre, which contains the cross; and the hole is the ring.
The bell towers are adorned with three inscriptions drawn from the liturgy of the Eucharist. The most visible of the three, placed halfway up, is the Tersanctus in Latin: Sanctus, Sanctus, Sanctus ('Holy, Holy, Holy'). Higher up, under the pinnacles, we see the words Hosanna and Excelsis written vertically ('Hosanna in Heaven,'if the phrase were complete). Lower down are the words Sursum Corda('Lift up your hearts'). Hence, the placement of the inscriptions follows the liturgical order.
This bell tower, dedicated to Barnabas the Apostle, was the only one Gaudí lived to see. Each bell tower is dedicated to an apostle, but not necessarily to one of the twelve original apostles. Barnabas is one of the exceptions, together with Saul of Tarsus (on the Glory façade), with whom he preached the Good News.
The figure of Barnabas, depicted in his seat, is flanked by a series of letters that spell his name and the word 'apostle'in Latin: Barnaba Apostolus.