Light is sown for the righteous, and gladness for the upright in heart. Light is sown for the righteous - The Divine light in the soul of man is a seed which takes root, and springs up and increases thirty, sixty, and a hundred fold. Gladness is also a seed: it is sown, and, if carefully improved and cultivated, will also multiply itself into thousands. Every grace of God is a seed which he intends should produce a thousand fold in the hearts of genuine believers. We do not so much require more grace from God, as the cultivation of what we have received. God will not give more, unless we improve what we have got. Remember the parable of the talents. Let the light and gladness be faithfully cultivated, and they will multiply themselves till the whole body shall be full of light, and the whole soul full of happiness. But it is the righteous only for whom the light is sown; and the upright in heart alone for whom the gladness is sown.
The words may also signify that, however distressed or persecuted the righteous and the upright may be, it shall not be always so. As surely as the grain that is sown in the earth shall vegetate, and bring forth its proper fruit in its season, so surely shall light - prosperity, and gladness - comfort and peace, be communicated to them. They also will spring up in due time.