John Calvin Commentary 1 Thessalonians 5:9

"For God appointed us not into wrath, but unto the obtaining of salvation through our Lord Jesus Christ," — 1 Thessalonians 5:9 (ASV)

For God has not appointed us. Since he has spoken of the hope of salvation, he elaborates on that topic and says that God has appointed us to this—that we may obtain salvation through Christ. The passage, however, might be explained simply in this way: that we must put on the helmet of salvation, because God does not will that we should perish, but rather that we should be saved. And Paul indeed means this, but, in my opinion, he has something further in view. For as the day of Christ is often regarded with alarm, he, intending to conclude with its mention, says that we are appointed to salvation.

The Greek term περιποίησις means enjoyment (so to speak) as well as acquisition. Paul undoubtedly does not mean that God has called us so that we may procure salvation for ourselves, but so that we may obtain it, as it has been acquired for us by Christ. Paul, however, encourages believers to fight strenuously, setting before them the certainty of victory; for the man who fights timidly and hesitatingly is half-conquered. In these words, therefore, he intended to take away the dread that arises from distrust. However, no better assurance of salvation can be gathered than from the decree of God. The term wrath, in this passage, as in other instances, is taken to mean the judgment or vengeance of God against the reprobate.