In times of testing be especially on your guard against certain sins

^14-17 Let it be your ambition to live at peace with all men and to achieve holiness “without which no man shall see the Lord”. Be careful that none of you fails to respond to the grace which God gives, for if he does there can very easily spring up in him a bitter spirit which is not only bad in itself but can also poison the lives of many others. Be careful too, that none of you falls into impurity or loses his reverence for the things of God and then, like Esau, is ready to sell his birthright to satisfy the momentary hunger of his body. Remember how afterwards, when he wanted to have the blessing which was his birthright, he was refused. He never afterwards found the way of repentance though he sought it desperately and with tears.