And it shall be, if he say unto thee, I will not go away from thee,.... Out of his house, nor quit his service:
because he loveth thee and thine house; his master and his family, and so loath to leave them, but chooses rather to stay with them than have his liberty; hence the Jews say (k), if his master has not a wife and children, his ear is not to be bored:
because he is well with thee; lives well with him, is well used by him, wants for nothing, and enjoys peace and quietness, and has everything to make him happy as such a state will admit of, and with the which he is well contented, and highly pleased. This is an emblem of the cheerful and constant obedience of the people of Christ to him their master, flowing from love to him; whom they love above all persons and things, with all their heart and soul, and his house also, the place of his worship, his ordinances, truths, ministers and children; and therefore choose to be where they are, finding that they are there well used, fare well, having bread enough and to spare, spiritual provisions in plenty; are well clothed with the righteousness of Christ, have the good company of the saints and excellent in the earth, in whom is all their delight; and, above all, the presence of their Lord and master, and the smiles of his countenance.
(k) Maimon. in Misn. Kiddushin, c. 1. sect. 2.

if he say unto thee, I will not go away from thee--If they declined to avail themselves of the privilege of release and chose to remain with their master, then by a peculiar form of ceremony they became a party to the transaction, voluntarily sold themselves to their employer, and continued in his service till death.

But if the man-servant and the maid-servant should not wish for liberty in the sixth year, because it was well with them in the house of their master, they were not to be compelled to go, but were to be bound to eternal, i.e., lifelong bondage, in the manner prescribed in Exodus 21:5-6.
(Note: Knobel's assertion, that the judicial process enjoined in Exodus 21:6 does not seem to have been usual in the author's own time, is a worthless argumentum e silentio.)
This is repeated from Ex 21, to guard against such an application of the law as might be really cruelty under the circumstances rather than love. Manumission was only an act of love, when the person to be set free had some hope of success and of getting a living for himself; and where there was no such prospect, compelling him to accept of freedom might be equivalent to thrusting him away.