Adam Clarke on 2 Thessalonians 2:15

Therefore, brethren, stand fast - Their obtaining eternal glory depended on their faithfulness to the grace of God; for this calling did not necessarily and irresistibly lead to faith; nor their faith to the sanctification of the spirit; nor their sanctification of the spirit to the glory of our Lord Jesus. Had they not attended to the calling, they could not have believed; had they not believed, they could not have been sanctified; had they not been sanctified they could not have been glorified. All these things depended on each other; they were stages of the great journey; and at any of these stages they might have halted, and never finished their Christian race.

Hold the traditions which ye have been taught - The word παραδοσις, which we render tradition, signifies any thing delivered in the way of teaching; and here most obviously means the doctrines delivered by the apostle to the Thessalonians; whether in his preaching, private conversation, or by these epistles; and particularly the first epistle, as the apostle here states. Whatever these traditions were, as to their matter, they were a revelation from God; for they came by men who spake and acted under the inspiration of the Holy Spirit; and on this ground the passage here can never with any propriety be brought to support the unapostolical and anti-apostolical traditions of the Romish Church; those being matters which are, confessedly, not taken from either Testament, nor were spoken either by a prophet or an apostle.