Charles Spurgeon Commentary Galatians 3:4-5

"Did ye suffer so many things in vain? if it be indeed in vain. He therefore that supplieth to you the Spirit, and worketh miracles among you, [doeth he it] by the works of the law, or by the hearing of faith?" — Galatians 3:4-5 (ASV)

Have you suffered so many things in vain? If it is indeed in vain. He therefore who ministers to you the Spirit, and works miracles among you, does he do it by the works of the law, or by the hearing of faith?

They knew very well that the miracles came as the result of faith, and were an attestation and seal of the gospel of faith, and not of the works of the law.