If you remember from the first half of Acts 17, Paul has been chased out of the previous two locations, Thessalonica and Berea, and was led by some trusted brothers to Athens to wait for Timothy and Silas. It turns out neither the Holy Spirit nor Paul was going to waste this opportunity to proclaim the gospel in one of the most cosmopolitan cities of that era. The absolute truth of the gospel has been brought to one of the most pluralistic societies to ever exist on the face of the earth.
So vv.16-18 contains all background information leading up to v.19 when he is led to the Areopagus. Interestingly enough, the last time Paul does anything, he is led to Athens in v.15. This means the missionary is still being directed providentially by the Holy Spirit through human means. It implies that he didn’t go to Athens to conform to their ways in order to make the gospel more acceptable to them. This becomes obvious in v.16 because notice what happens to Paul as he is waiting in Athens—he was provoked in his spirit. He was severely agitated or irritated. This kind of agitation in the Lord is what ushers in his wrath many times in the OT. Even though the word is not used in the gospels, it’s this same type of disposition that is present in our Lord when he cleansed the temple from its wicked practices during his earthly ministry.
Ultimately, Paul was disgusted by the city overrun by idol worship in Acts 17. This is directly linked to the primary motive for evangelism and missions. Compassion for souls is a great motive for sharing the gospel, but it is always secondary to the greatest motive, namely that the one true God would get the glory He deserves. The gospel needs to go forth primarily because the Triune God is not feared and honored by all of his created beings. Thus Paul’s provoked state was due to God’s name being trashed throughout this city and so he gave the Athenians clear teaching on the character of God and the gospel of repentance. It’s this commitment to God’s glory, which prevents us from deviating from faithful Christianity.