On the tenth day after Jesus' ascension, Holy Spirit did descend to give disciples power to witness for the Lord's resurrection.
But all the training in the world won't motivate you to witness for Christ until you internalize the eight convictions covered in the previous chapter.
When a person is not sure of his salvation he is not able to serve Christ or to witness for him as he should.
In order to learn how to discharge your duty as a witness for Christ, look at his example.