5 Now to this the example of Issachar, the patriarch, may persuade, as the Scripture says, 'Issachar desires that which is good, resting between the heritages; and when he saw that the rest was good, and the land fertile, he bowed his shoulder to labour, and became a husbandman.' Being consumed by divine love, like the spouse in the Canticles, he gathered abundance from the holy Scriptures, for his mind was captivated not by the old alone, but by both the heritages.
And hence as it were, spreading his wings, he beheld afar off 'the rest' which is in heaven, and—since this 'land' consists of such beautiful works—how much more truly the heavenly [country] must also [consist] of such; for the other is ever new, and grows not old. For this 'land' passes away, as the Lord said; but that which is ready to receive the saints is immortal. Now when Issachar, the patriarch, saw these things, he joyfully made his boast of afflictions and toils, bowing his shoulders that he might labour.
And he did not contend with those who smote him, neither was he disturbed by insults; but like a strong man triumphing the more by these things, and the more earnestly tilling his land, he received profit from it. The Word scattered the seed, but he watchfully cultivated it, so that it brought forth fruit, even a hundred-fold.
Source: Letters (New Advent)