And when thou sendest him out free from thee, thou shalt not let him go away empty:

Jamieson-Fausset-Brown Bible Commentary

13-15. thou shalt not let him go away empty-A seasonable and wise provision for enabling a poor unfortunate to regain his original status in society, and the motive urged for his kindness and humanity to the Hebrew slave was the remembrance that the whole nation was once a degraded and persecuted band of helots in Egypt. Thus, kindness towards their slaves, unparalleled elsewhere in those days, was inculcated by the Mosaic law; and in all their conduct towards persons in that reduced condition, leniency and gentleness were enforced by an appeal which no Israelite could resist.

Matthew Henry's Concise Commentary

15:12-18 Here the law concerning Hebrew servants is repeated. There is an addition, requiring the masters to put some small stock into their servants' hands to set up with for themselves, when sent out of their servitude, wherein they had received no wages. We may expect family blessings, the springs of family prosperity, when we make conscience of our duty to our family relations. We are to remember that we are debtors to Divine justice, and have nothing to pay with. That we are slaves, poor, and perishing. But the Lord Jesus Christ, by becoming poor, and by shedding his blood, has made a full and free provision for the payment of our debts, the ransom of our souls, and the supply of all our wants. When the gospel is clearly preached, the acceptable year of the Lord is proclaimed; the year of release of our debts, of the deliverance of our souls, and of obtaining rest in him. And as faith in Christ and love to him prevail, they will triumph over the selfishness of the heart, and over the unkindness of the world, doing away the excuses that rise from unbelief, distrust, and covetousness.