Short answer: The most likely author of Amos 5:14–15 is the prophet Amos himself — Amos of Tekoa — and evangelicals understand him as an 8th-century BC prophet sent by God to call Israel to repentance, justice, and covenant faithfulness.

Key facts (evangelical perspective)
– Author identity: The book itself names its author (Amos 1:1), and Amos later describes his own background (Amos 7:14–15). Evangelicals take these self-identifications seriously: “Amos, who was among the shepherds of Tekoa” (a Judean village).
– Background and occupation: Amos was a shepherd, herdsman, and “dresser of sycamore trees” (or “plumb-line”/fig-grower depending on translation) — not a professional court prophet, which underscores his humble origins and the divine nature of his calling.
– Date and audience: He prophesied during the reigns of Uzziah of Judah and Jeroboam II of Israel (roughly 760–750 BC). Though a Judean by birth, his primary audience was the Northern Kingdom (Israel), especially its cities and elites.
– Authorship and inspiration: Evangelicals affirm that Amos’s messages are God‑given prophecy (frequently introduced with “Thus says the LORD”) and generally accept the book as largely the prophet’s own words, preserved under divine inspiration. Some evangelical scholars allow for minor editorial framing but maintain Amos as the primary author and source.

Historical and theological context
– Political/religious setting: A time of material prosperity in Israel but also of social injustice, corruption, and empty ritual. Amos’s prophecies confront the gap between religious observance and moral failure.
– Central themes reflected in 5:14–15:
– Call to repentance and seeking the LORD (“Seek good and not evil…”).
– Commitment to justice and righteousness as expressions of true faith (“…establish justice in the gate”).
– The hope that God might be gracious to the remnant — covenant mercy conditioned on repentance.
– Covenant framework: Amos’ indictment assumes Israel’s covenant relationship with Yahweh — ritual without righteousness violates the covenant and brings judgment unless there is genuine turning to God.

Why Amos 5:14–15 matters to evangelicals
– It links personal repentance to social ethics: genuine turning to God issues in loving what is good, hating evil, and establishing justice. Evangelicals often cite Amos as biblical warrant for combining evangelism with concern for justice and mercy.
– It underscores that God’s displeasure is not primarily with worship forms but with a people living in disobedience; worship must be matched by holiness (cf. Micah 6:8).
– It models prophetic courage and the priority of God’s truth over social standing — an example for believers called to speak truth lovingly but boldly.

A brief look at the verses (NIV paraphrase)
– Amos 5:14–15 urges seeking the good, hating evil, and acting in ways that preserve life and invite God’s mercy — a succinct ethical summons grounded in covenant faithfulness.

If you’d like, I can:
– Give a short exposition of Amos 5:14–15 verse-by-verse from an evangelical point of view;
– Provide cross-references (e.g., Micah 6:8, Isaiah, New Testament parallels);
– Suggest modern applications for church and personal life. Which would help most?