Matthew 20:2

And when he had agreed with the labourers for a penny a day, .... These labourers were of that sort that were called שכיר יום , "hired for a day"; concerning whom is the following rule F17 Misna Bava Metzia, c. 9. sect. 11. Maimen Hilch. Shericut, c. 11. sect. 2. :

"he that is hired for a day, may demand it all the night; and he that is hired for a night may demand it all the day: he that is hired for hours, may demand it all the night, and all the day; he that is hired for a week, he that is hired for a month, he that is hired for a year, he that is hired for seven, if he goes out in the day, may demand all the day; and if he goes out in the night, he may demand it all the night, and all the day.'

And the wages of a day were usually דינר "a penny"; which, if understood of a Roman penny, was seven pence halfpenny of our money. One of their canons runs thus F18 Maimon. Hilch. Milvah Ulavah, c. 7. sect. 12. Vid. T. Bab. Bava Bathra, fol. 86. 2. & 87. 1. & Gloss. in ib. :

"he that hires a labourer in the winter, to work with him in the summer, בכל יום , "for a penny every day", and he gives him his hire; and, lo! his hire is alike to that in the winter, a "sela" every day, this is forbidden; because it looks as if he chose that time to lessen his wages; but if he says to him, work with me from this day, to such a time, "for a penny every day", though his hire is the same, a "sela" every day, this is lawful.'

By the penny a day agreed for with the labourers, may be meant external privileges; or the free promise made, whether to ministers, or private believers, of a sufficient supply of grace daily, that as their day is, their strength shall be; together with that of eternal life and happiness at last.

He sent them into his vineyard; to labour there: for none have any business there, but such who are called and sent by the owner of it; and where sons are sent, and work, as well as servants; see Matthew 21:28 .