Galatians 5:4

Then when he says, "You are made void of Christ," he proves what he said, namely, that they must not embrace the observances of the Law, because it involves a double injury: first, the loss of Christ; secondly, the loss of grace. Moreover, the first …

That is, you have no communion with Christ: you who think to obtain justification in the law have fallen from grace, which truly justifies. It is a great misfortune when you will not receive what the law promises, and you lose what grace gives.

Therefore Christ is become of no effect to you - Who seek to be justified by the law. Ye are fallen from grace - Ye renounce the new covenant. Ye disclaim the benefit of this gracious dispensation.

Christ is become of no effect unto you,....

How they hope to obtain this happiness, namely, by faith, that is, in our Lord Jesus Christ, not by the works of the law, or any thing they can do to deserve it, but only by faith, receiving and relying upon him as the Lord our righteousness. It is in this way only that they expect either to be entitled to it here or possessed of it hereafter.

Christ is become of no effect unto you - It is vain for you to attempt to unite the two systems. You must have the law and no Christ, or Christ and no law, for your justification. Ye are fallen from grace - From the Gospel. They had been brought into the grace of the Gospel; and now, by readopting the Mosaic ordinances, they had apostatized from the Gospel as a system of religion, and had lost the grace communicated to their souls, by which they were preserved in a state of salvation.

Ro 7:2, "Loosed from the law," where the same Greek occurs as here. whosoever of you are justified--"are being justified," that is, are endeavoring to be justified. by the law--Greek, "IN the law," as the element in which justification is to take place. fallen from grace--Ye no longer "stand" in grace (Ro 5:2).

Christ is become of no effect unto you - You will derive no advantage from Christ. His work in regard to you is needless and vain. If you can be justified in any other way than by him, then of course you do not need him, and your adoption of the other mode is in fact a renunciation of him. Tyndale renders this: “Ye are gone quite from Christ.” The word here used (καταργέω katargeō), means properly, to render inactive, idle, useless; to do away, to put an end to; and here it means that they had withdrawn from Christ, if they attempted to be justified by the Law. They would not need him if they could be thus justified; and they could derive no benefit from him. A man who can be justified by his own obedience, does not need the aid or the merit of another; and if it was true, as they seemed to suppose, that they could be justified by the Law, it followed that the work of Christ was in vain so far as they were concerned. Whosoever of you are justified by the law - On the supposition that any of you are justified by the Law; or if, as you seem to suppose, any are justified by the Law. The apostle does not say that this had in fact ever occurred; but he merely makes a supposition. If such a thing should or could occur, it would follow that you had fallen from grace. Ye are fallen from grace - That is, this would amount to apostasy from the religion of the Redeemer, and would be in fact a rejection of the grace of the gospel. That this had ever in fact occurred among true Christians the apostle does not affirm unless he affirmed that people can in fact be justified by the Law, since he makes the falling from grace a consequence of that. But did Paul mean to teach that? Did he mean to affirm that any man in fact had been, or could be justified by his own obedience to the Law? Let his own writings answer; see, especially, Rom 3:20. […]