Bl. Jacobus de Voragine - "Golden Legend" - "The Ten Commandments' interpretation from Middle Ages - part I"

"The first commandment that God commanded is this. Thou shalt not worship no strange ne diverse gods. That is to say, thou shalt worship no god but me, and thou shalt not retain thine hope but in me, for who that setteth principally his hope on any creature or faith or belief in any thing more than in me, sinneth deadly. And such be they that worship idols, and make their god of a creature; whosoever so doth, sinneth against this commandment. And so do they that overmuch love their treasures, gold or silver, or any other earthly thing that be passing and transitory, or set their heart or hope on any thing by which they forget and leave God their creator and maker which hath lent to them all that they live by. And therefore ought they to serve him with all their goods, and above all things to love him and worship him with all their heart, with all their soul, and with all their strength, like as the first commandment enseigneth and teacheth us.

The second commandment is this, that thou shalt not take the name of God in vain, that is to say, thou shalt not swear by him for nothing. In this commandment our Lord commandeth in the gospel that thou shalt not swear by the heaven ne by earth ne by other creature. But for good cause and rightful a man may swear without sin, as in judgment or in requiring of truth, or without judgment in good and needful causes. And in none other manner without reason by the name of our Lord and for nought. If he swear false wittingly he is forsworn, and that is against the commandment and sinneth deadly, for he sweareth against his conscience, and that is when he sweareth by advice and by deliberation, but a man should swear truly and yet not for nought or for any vain or ill thing, ne maliciously. But to swear lightly without hurt or blame is venial sin, but the custom thereof is perilous and may well turn to deadly sin but if he take heed. But he then that sweareth horribly by our Lord, or by any of his members, or by his saints in despite, and blasphemeth in things that be not true, or otherwise, he sinneth deadly, he may have no reason whereby he may excuse him. And they that most accustom them in this sin they sin most, etc.

The third commandment is that thou have mind and remember that thou hallow and keep holy thy Sabbath day or Sunday. That is to say, that thou shalt do no work nor operation on the Sunday or holy day, but thou shalt rest from all worldly labour and intend to prayer, and to serve God thy maker, which rested the seventh day of the works that he made in the six days tofore, in which he made and ordained the world. This commandment accomplisheth he that keepeth to his power the peace of his conscience for to serve God more holily. Then this day that the Jews called Sabbath is as much to say as rest. This commandment may no man keep spiritually that is encumbered in his conscience with deadly sin, such a conscience can not be in rest ne in peace as long as he is in such a state. In the stead of the Sabbath day which was straitly kept in the old law, holy church hath established the Sunday in the new law. For our Lord arose from death to life on the Sunday, and therefore we ought to keep it holily, and be in rest from the works of the week tofore, and to cease of the work of sin, and to intend to do ghostly works, and to follow our Lord beseeching him of mercy and to thank him for his benefits, for they that break the Sunday and the other solemn feasts that be stablished to be hallowed in holy church, they sin deadly, for they do directly against the commandment of God aforesaid and holy church, but if it be for some necessity that holy church admitteth and granteth. But they sin much more then, that employ the Sunday and the feasts in sins, in lechery, in going to taverns in the service time, in gluttony and drinking drunk, and in other sins, outrages against God. For alas for sorrow I trow there is more sin committed on the Sunday and holy days and feasts than in the other work days. For then be they drunk, fight and slay, and be not occupied virtuously in God's service as they ought to do. And as God commandeth us to remember and have in mind to keep and hallow the holy day, they that so do sin deadly and observe and keep not this third commandment. These three commandments be written in the first table and appertain only to God."

Philippe de CHAMPAIGNE - Moses with the Ten Commandments: