James 1:25 But whoso looketh into the perfect law of liberty, and continueth therein, he being not a forgetful hearer, but a doer of the work, this man shall be blessed in his deed.
James had just wtitten about hearers of the Law and not doers of it: they look at their face in a mirror and then walk away and forget what they looked like. The Law is like a mirror that reflects the self and shows our Sin. If we do not respond in repentance we are not a doer, but a forgetter.
Here in this verse God gives a promise of blessedness for the person who does the Law by responding in repentance and faith with a sincere desire to change his way. The “perfect law of liberty” is the whole counsel of God, both Law and Gospel. It shows how Jesus died for your sins, kept the Law for you, and freely grants forgiveness and righteousness. And all who repent and believe the Gospel are doers of the work. These respond with the deed of repentance and faith. In John 6:28, they asked Jesus, “What must we do?” Jesus answered, ”This is the work of God, that you believe [in Me],”
This Gospel (the perfect law of liberty) is the power of God to save and to effectively change our lives for the better. This is the promised blessing.