From syn (together, intensifier) + tēreō (to keep, guard). Syntēreō means to preserve, protect, keep safe, treasure carefully. Used of Herod guarding John the Baptist (Mark 6:20), the new wine preserved in new wineskins (Luke 5:38), and Mary treasuring things in her heart (Luke 2:19).
The most theologically luminous use of syntēreō is in Luke 2:19: 'But Mary treasured up (synēterei) all these things and pondered them in her heart.' In the midst of the extraordinary events of Jesus' birth — shepherds arriving with angelic proclamations, descriptions of the Messiah — Mary's response was not to immediately publicize or theologize but to guard and ponder. Syntēreō is the verb of deep, careful interior keeping — like placing something precious in a vault and turning it over slowly in the mind and heart. This models the Christian's proper response to divine revelation: not mere intellectual acknowledgment but contemplative, guarding meditation. The word appears again in Luke 5:38 for new wine in new wineskins — the wineskins must be flexible enough to expand with the wine's fermentation while syntēreō-ing (preserving) the wine itself. The kingdom's new wine requires a container (heart, community) that can guard what God is doing while allowing it to expand.