A missionary priest assigned in his hometown noticed Arce’s gift for music and, wanting to encourage him, helped put him through college as a working student. Arce became a teacher, eventually becoming principal (and bandmaster) of the missionary-run Little Flower High School in Peñarrubia, Abra.
But he stayed a farmer, helping his father (who also played in the town band) in tending the fields of corn and sugarcane after school hours. He also served as a lay leader in the Catholic parish in Peñarrubia. Later he was elected president of the Samahang Nayon and the Irrigators Service Association in his home village of Agtangao, Bangued.
Arce had gone to college in the 1960s, when nationalist ferment was creating a progressive intellectual environment that helped mold his thinking.
In the early 1970s, Arce joined the Federation of Free Farmers (FFF) and later became its provincial coordinator for Abra. Under his leadership and with the help of other priests and nuns in the province, FFF conducted seminars for the farmers and organized local cooperatives. Landlords harassed their activities, but Arce remained convinced about the need to reform the tenancy system in the rural areas. The local martial-law authorities did not appreciate his activities either.
In 1974, Arce was implicated in the murder of a police informer. The murder suspect had told investigators that the school principal was the owner of the motorcycle used in the killing. Santiago was arrested but released on the same day on the intervention of the seminary rector of the Society of the Divine Word in Bangued. He was arrested again two days later. Afterwards, residents living close to the military camp reported hearing during the night Arce’s agonized moans and pleas for his life. He was shot dead a few hours later for “trying to escape.”
Arce was buried after the longest and biggest funeral procession ever recorded at the time in Abra, despite the pervasive fear of retaliation from the martial-law authorities. Classes in Catholic schools all over the province were suspended so teachers and students could attend it. Twenty priests concelebrated a funeral mass.
At the height of the Marcos dictatorship’s repression, such a public display of unity was uncommon. It was because, as a friend said, Arce was well respected: “Mahal siya ng tao. Kahit sa mga hindi member ng FFF kilala siyang mabuting tao.Napaka-useful sa community. Maraming naituturo.” (The people loved him Even those who were not FFF members looked up to him as a good man. He was so useful to the community. He was able to teach many things.)