So shall they be life unto thy soul,.... Give it a better life than it naturally has, though immortal; Christ is both the spiritual and eternal life of the souls of those that look unto him by faith; and his Gospel, and the doctrines of it, are the means of reviving drooping saints, and of quickening them to the discharge of their duty; wherefore both he and they should be kept in continual view, and held fast;
and grace to thy neck; an ornament to that and to the whole man; how ornamental is Christ and his righteousness to a believer! how lovely is the person that is steady in his principles, and regular in his practices! who stands fast in the truths of the Gospel, and whose conversation is as becomes it! see Proverbs 1:9.

assign reasons in their value for happiness and ornament, guidance and support in dangers, both when waking and sleeping.

Grace - Like a beautiful chain or ornament.