Mark 13:9

“But beware for yourselves. For they will deliver you up to councils and you will be beaten in synagogues, and you will stand before governors and kings for my sake, for a testimony to them.”

We should note by these words that Jesus was indicating how successful their work was going to be, (kings and governors only have drawn to their attention things that are important), but warning that it would be accompanied by constant censure. They were going to draw attention to themselves in the eyes of the authorities. Their ministry would be such that it would not only bring them to the attention of the local sanhedrins and the synagogues, resulting in the usual beating given to heretics, but would also disturb governors and kings. And this would all be part of their testimony. The descriptions give the idea of a widespread ministry reaching even to exalted circles. The book of Acts reveals how accurate Jesus' words would prove to be.

‘A testimony to them.' Through their trials even great men would hear the word of life. And that word would either begin to enlighten them or would testify against them at the Judgment.

These words parallel those spoken by Jesus in the passage where He sent His disciples out to preach (Matthew 10:17). There too they had been successful and had drawn attention to themselves and their message, and we need not doubt had been beaten in synagogues and brought before local councils (Luke 12:11). But in those words Jesus had also had in mind their later wider ministry, as depicted here, for they were to be ‘a testimony to the Gentiles' (Matthew 10:18). Thus it seems that by this time if not before Jesus had recognised that there would be a ministry among Gentiles (but compare Matthew 8:11 which suggests a recognition long before). Matthew had very much in mind the gradual turning to the Gentiles.