Those under the law are every unredeemed human being. Jews received the written law through Moses (Romans 3:2), and Gentiles have the works of the law written on their hearts (Romans 2:15), so that both groups are accountable to God. There is no defense against the guilty verdict God pronounces on the entire human race.
Commentary from the MacArthur study Bible, notes for Romans 3:19.
If a baby cries in the middle of the night, or soils a diaper, or spits up food, over knocks over a priceless vase, the parents love that child anyway, because they love the child unconditionally. But somewhere along the line, parents’ unconditional love often gets harder. At some point they hear themselves saying, “You know better!” Parents are tempted to love “because of” instead of “in spite of.”
Children who are raised with conditional love have a challenge ahead: understanding God’s unconditional love. God’s love is the same whether we are immature and sin, or whether we are mature and sin. His love is always unconditional.
Portions of commentary from David Jeremiah’s Turning Points Devotional, December 8, 2016.