BE JUST: In this context, the word "justly" means "to do what is right according to God's Law." When we obey God's Law, we are, in actuality, obeying God's will for our lives. And what is God's will? It is stated in Galatians 5:14: "For ALL the Law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself." If we truly love someone, we will not murder them, steal from them, lie about them, etc., but we will treat them as we ourselves wish to be treated. Being just is obeying God's Golden Rule! We need to be more like Jesus!
BE MERCIFUL: "Mercy," as it is used in this verse, means "to have pity" (see Mt. 9:27; 15:22; 17:15; 20:30-31; etc.). Here again, God's Golden Rule applies. Jesus spoke of our treating others with mercy (forgiveness) because we have received His mercy, that is, His forgiveness (Mt. 6:12-15; 18:21-35; etc.). Most of us eventually forgive someone who has wronged us, but few, if any, actually "love" forgiving; our natural inclination is resentment at our best, and revenge at our worst. We need to be more like Jesus!
BE HUMBLE: Here, the word "humbly" means "to walk or live modestly, or to recognize one's lowly estate." If we compare ourselves to those around us, we usually feel we fall somewhere between those who appear to be the most spiritual, and those who appear to be down-right evil. But, when we recognize our lowly estate, that there is nothing good about us, that our salvation is a gift and not something we have earned (Rom. 3:23; 6:23; Eph. 2:8-9), we cannot help but be humbled! We certainly will not think more highly of ourselves than we ought (Rom. 12:3). And, we WILL BE more like Jesus (Phil. 2:3-8)!
What is God's will for your life? Be like Jesus!