Major and Minor Shields are rituals, available to (now) all priests.

They protect you by reducing damage of each blow you suffer by some amount of hp (more for Major, less for Mminor). That amount is considerably large, effectively meaning that only specials can harm someone, protected with Major Shield. duration of that effec is about one second for each bonus point in faith.rituals.defensive.self/target skill.

Performing Shiled ritual repeatedly with same skill does not make it stronger, but increase it's duration.

Exact rules of stacking Major and Minor Shields is not known.

Minor: Base cost 90G. A holy symbol is needed. Granted on level 25 in faith.rituals.misc.defensive.target.

Major: Base cost 120G. A holy symbol is needed. Granted on level 79 in faith.rituals.misc.defensive.target.

Target - self or any living thing. Not PK-checked, but casting it by NPK on PK in fight with another PK is a forbidden PK/NPK interaction.