The symbolic and striking features of the cathedral are not only found outside but also within. In keeping with the contemporary and modern design of the cathedral, the interior decor likewise reflects this concept. The interior design is at once bold, outstanding and unconventional to the observer. The decor is indeed unique in the whole of Sabah. Behind the sacred artwork are symbolic meanings which many people are not aware of. Essentially they draw one’s thoughts and attention to Christ and God. As a cathedral it deserved the best but affordable design befitting its status as the mother church of the diocese.
a) The Cathedral
i) The Mosaic Mural
When one enters a typical church, a huge crucifix usually hangs behind the altar. However, in Sacred Heart, it is not the cross that one sees. When one enters the cathedral, a huge mural (20 ft x 20 ft) behind the altar immediately catches the eye. As the main feature, the mural depicts Jesus Christ risen, amiable and triumphant, just over the shores of Sabah with Mt Kinabalu – Sabah’s highest mountain – in the near distance. The mural depicts our Christian faith – which is in the One who is risen from the dead. This stunning masterpiece is made up of thousands of pieces of colourful mosaic. At a distance, the mosaic mural looks just like a painting. It is probably the only kind to be found in Sabah.
ii) The Way of the Cross
Unlike the conventional fourteen individually placed Stations of the Cross, the cathedral’s depiction is done over four sections. The painful story of Calvary carved in iron lines, modern, simple and sorrowful, covers a length of 63 feet of the back walls of the cathedral, facing the congregation. They are beautifully and skillfully constructed.
iii) The Windows
The windows of the cathedral featured the new media of sacred art – fibreglass. The tall and narrow panes on the left of the cathedral depict the eucharistic theme of wheat while the ones on the right that of grapes and vines. They are symbols of spiritual food which is Christ himself – bread and wine, the Eucharist. Though not as glorious and beautiful as stained glass, these fibreglass windows have a beauty of their own. Unfortunately, the original windows at the front of the cathedral were left out of the designs. These windows were changed in 1996 when more windows were added for better ventilation.
b) The Blessed Sacrament Chapel
i) The Tabernacle
The tabernacle of the cathedral is unusually placed in that it is actually inside the chapel, separated from the main building by a long timber wall paneling which can be opened at the centre to access it from the cathedral side. The tabernacle is a monument made of marble and is designed around the altar. A beautiful and colourful mosaic mural depicting fish, bread, wine, grapes and wheat – spiritual food – decorate the front of the sacred repository.
ii) Iron Murals
Two iron murals on both sides of the wall guide one’s thoughts towards the holy Eucharist. The first depicts Moses opening 
the Red Sea, strikes water from the rock in the middle of the desert and collection of manna from the sky which is symbolic of the Eucharist. The right side iron mural depicts the repentance and acceptance of the prodigal son. Miserable among pigs and clothed in rags, he rushes back home to his father who is halfway already waiting for him. At the end the big feast of the return, roasting the fattened calf and restoring back his cape and ring.
iii) The Baptismal Pool
The pool was fashioned after those used during the early days of Christian communities when those who took baptismal vows were required to submerge themselves. The pool had seven steps down on each side with “running water” at the centre.
It was in the flowing waters of the Jordan River that Jesus was baptised. Now in the pool of running waters of the cathedral the neophytes are submerged to symbolic death in order to rise up alive filled with the Holy Spirit. The fibreglass window depicts the story of the river and Jesus, and a huge dove, symbol of the Holy Spirit, embraces Jesus and the river and the whole world … Beautiful oriental lotus springing from the bottom represents the new life to bloom in joy and peace of Jesus the Lord.
The artwork in this large fibreglass window is today obstructed by safety grills. The pool is no longer used and has been sealed over as baptism is now carried out in a new baptismal pool inside the main cathedral before the sanctuary.
The person responsible for the magnificent artwork was a Mexican artist, Francisco Borboa, who was the resident of Taiwan. He came to Fr Chi to offer his services. The contract was signed in June 1981 with Borboa Mosaic and Designes for US$64,000 (excluding freight and insurance). Borboa came to Sacred Heart to oversee the installation of the artwork.
c) The new baptismal font
The first and original baptismal font was placed in the Blessed Sacrament Chapel. The place was small and cosy enough for parents and their babies getting baptised. It was probably the first baptismal pool to be constructed in Malaysian Catholic churches. Baptism by immersion soon became the norm in Sacred Heart for both infants and adults.
However, over the years the baptismal font area became too congested, thanks to a burgeoning Catholic population in the 1980s and 1990s. A new font had to be constructed and it was to be in the cathedral. The responsibility fell on Fr CosmasLee. In 1995 a new below ground baptismal font was planned. It was completed in February 1998.
Situated in front of the altar, the octagonal design of the fibreglass covers of the baptismal font was “neo” inspired. Assisted by Fr Pipo and Fernando Valdes of the Spanish neo-catechumenate, Fr Lee enlisted the services of architect Mattia del Prete of Rome to design the covers. The covers were done in Venice and then air-freighted over.
The octagonal covers are mosaic murals depicting the symbols of the four gospels: eagle (John), man (Matthew), lion (Mark), ox (Luke). The cost of the design was US$21,950. The cost of the construction font by Ngoh Contractor was about RM55,000.
As a parish and as the archbishop’s church, the cathedral building symbolises the Catholic faith of the archdiocese. It is therefore very important that the spiritual life of the cathedral parish be strong, active and dynamic as it leads the way for other parishes in the archdiocese to follow. – Stella Moo-Tan, Silver Jubilee of the Dedication of Sacred Heart Cathedral, 2006.