"We are surrounded by a so great crowd of witnesses…" probably meant those who had been martyred for their faith in Christ. Other scholars think it meant their ancestors in the Jewish faith.
The phrase connects with the next verse that talk about running a race, keeping one's eye on the goal and persevering to the finish. In the Greco-Roman world, runners were encouraged by the huge crowd gathered in the stadium watching the race. Runners would strip themselves of anything that might encumber them. The goal of the Christian is Jesus, urging the person to strain further. We are not alone in our struggle.
However, we are not to glorify suffering. Some suffering is caused by structures and systemic sin and evil, such as racism, sexism, classism, and homophobia. Being uncritical of suffering only perpetuates structural and systemic evil.
Did Jesus really say: I have come to light a fire on the earth."? Did he really say: "I have come to bring division."? The Jesus who came to bring peace. The division would be brought about by the coming judgment, the challenge of the new age. In the gospel according to John he says that Jesus will baptize with the Holy Spirit and fire. The divisions had already started when these gospels were written. Many Christians had been thrown out of the synagogues. It may also have referred to the suffering and death Jesus himself would feel. It would be physical suffering but also personal when relationships would be severed when disciples would choose to follow his way.
Maria McClain, RCWP