If therefore by grace. This argument is similar to the preceding one, or nearly so. "As it is owing to the kindness of God that all things are lawful for me, why should I act in such a manner, that it should be reckoned to my account as a vice?" We cannot, it is true, prevent the wicked from reviling us, nor even the weak from being sometimes displeased with us; but Paul here reproves the forwardness of those, who of their own accord give occasion of offense, and hurt weak consciences, when neither necessity or expediency calls for it. He would have us, then, make a good use of our benefits, [1] that the weak may not have occasion of reviling from our inconsiderate use of liberty.

Footnotes

1 - "C'est a dire, de nestre liberte;" -- "That is to say, of our liberty."

For if I by grace be a partaker - Or rather, "If I partake by grace; if by the grace and mercy of God, I have a right to partake of this; yet why should I so conduct as to expose myself to the reproaches and evil surmises of others? Why should I lay myself open to be blamed on the subject of eating, when there are so many bounties of Providence for which I may be thankful, and which I may partake of without doing injury, or exposing myself in any manner to be blamed?"
Why am I evil spoken of - Why should I pursue such a course as to expose myself to blame or censure?
For that for which I give thanks - For my food. The phrase "for which I give thanks" seems to be a periphrasis for "food," or for that of which he partook to nourish life. It is implied that he always gave thanks for his food; and that this was with him such a universal custom, that the phrase "for which I give thanks" might be used as convenient and appropriate phraseology to denote his ordinary food. The idea in the verse, then, is this: "By the favor of God, I have a right to partake of this food. But if I did, I should be evil spoken of, and do injury. And it is unnecessary. God has made ample provision elsewhere for my support, for which I may be thankful. I will not therefore expose myself to calumny and reproach, or be the occasion of injury to others by partaking of the food offered in sacrifice to idols."

For if I by (y) grace be a partaker, why am I evil spoken of for that for which I give thanks?
(y) If I may through God's grace eat this meat or that meat, why should I through my fault cause that benefit of God to turn to my blame?

For if I by grace be a partaker,.... Either of Christian liberty, through the grace of God; or of the creatures God has given men to eat of through his goodness, and which are enjoyed by the saints with thankfulness:
why am I evil spoken of for that for which I give thanks? that is, why should I expose myself to evil tongues, the blasphemies and reproaches of men, by eating things of this kind, under this circumstance, when there are so many creatures I can use without offence, and be thankful for? or why should my liberty be reproached through an imprudent use of it, for which I have the utmost reason to be thankful? wherefore upon the whole it is best to deny one's self in such a case, rather than risk one's character, the glory of God, and the honour of religion.

For--The oldest manuscripts omit "For."
by grace--rather, "thankfully" [ALFORD].
I . . . be partaker--I partake of the food set before me.
evil spoken of--by him who does not use his liberty, but will eat nothing without scrupulosity and questioning whence the meat comes.
give thanks--which consecrates all the Christian's acts (Romans 14:6; 1-Timothy 4:3-4).

If I by grace am a partaker - If I thankfully use the common blessings of God.