Magic Vestment spell says you can imbue a suit of armor OR a shield with an enhancement bonus. So, you must decide which armor or which shield you imbue with the bonus. Lets say I decide my nom magic full plate armor. By casting second magic vestment spell I decide to imbue my new masterwork non magical heavy steel shield. Will the spells operate both?
You imbue a suit of armor or a shield with an enhancement bonus of +1
Casting it on a suit of full plate and a shield gives you a +1 Full Plate and a +1 shield.
Enhancement bonuses on armour gives it an increase to Armour Bonus, and shields to Deflection, which stack.
This would not stack if the spell gave a specific bonus, such as giving a Deflection or Armour bonus to an item, thus giving you a shield and armour with the same magical bonus.
But as Magic Vestment gives them an Enhancement bonus, the normal rules for enchanted equipment applies, and a cast on each item will stack.