Since his comments on Galatians 5:6 are relatively short, at the end of them I will provide a list to my former posts about these two world-changing books (Galatians and Luther's commentary on it)... Perhaps you might want to click on one or a few and discover or review them before we move on.
Here's what the great Reformer had to say about verse 6 of Galatians 5...
VERSE 6. For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision, but faith which worketh by love.
Faith must of course be sincere. It must be a faith that performs good works through love. If faith lacks love it is not true faith. Thus the Apostle bars the way of hypocrites to the kingdom of Christ on all sides. He declares on the one hand, "In Christ Jesus circumcision availeth nothing," i.e., works avail nothing, but faith alone, and that without any merit whatever, avails before God. On the other hand, the Apostle declares that without fruits faith serves no purpose. To think, "If faith justifies without works, let us work nothing," is to despise the grace of God. Idle faith is not justifying faith. In this terse manner Paul presents the whole life of a Christian. Inwardly it consists in faith towards God, outwardly in love towards our fellow-men.
And here are the titles and links for my previous posts on Galatians and Luther, in case you'd like to check out any of them...
Martin Luther: "Preach the Gospel to Yourself" (from his commentary on Galatians 1:1-4)
What Martin Luther would say to Donald Trump (from his commentary on Galatians 4:12-20)
Was Luther an Antinomian? (from his commentary on Galatians 4:21-31)