The church stands on the western edge of Stora alvaret, an area rich in prehistoric remains, including four unusually large megalithic tombs. Building archaeology has traced the oldest sections — the apsidal chancel, the nave and parts of the west tower — to the late eleventh century, with the west tower completed around the mid-twelfth century. An east tower was added around 1200, giving the church a distinctive twin-towered profile for several centuries, before being reduced almost to the level of the original chancel during rebuilding in 1826.
Resmo is considered one of the best-preserved medieval churches on Öland, and it is thought to have also served a defensive function at times, a detail that adds an intriguing layer to its otherwise modest, ancient appearance. Look out for the north doorway, its inner opening now walled up, which is topped by unusually long oak lintels in a form found in Sweden only on Öland, notably also at Ventlinge church.
Inside, the church holds Öland's largest surviving group of Romanesque wall paintings. The earliest, from the mid-twelfth century, depicts the Majestas Domini in the vault of the apse; a more extensive sequence in the high triumphal arch and on the west side of the triumphal wall dates from around 1200. Later fragments survive from the mid-thirteenth and late sixteenth centuries, giving visitors a rare chance to see several centuries of decoration in one small building.
Most of the furnishings visible today date from the late eighteenth century. The altarpiece, with its triangular pediment, and the pulpit were both made in 1799 by Carl Fredric Sundvall in a strict, antiquarian style that had recently come into fashion in Sweden. The church's tunnel-vaulted wooden ceiling, tall pointed windows and narrow, high nave are largely the result of alterations made in the 1780s and again in 1826, when the building took on much of its present external appearance.