Game rule not working. when I play a sorcery (Vanquish the Horde), the game dont let me play a creature with flash (Guardian of the Faith). The sorcery resolves instantly and dont give me the oportunity to play the spell "Guardian of the Faith"

Situation:
I have 4 plains and 1 island, and there are more than 5 creatures in the battlefield (so Vanquish the Horde costs 2 white mana to play)
Steps are:
1. During the 1st main phase, i play "Vanquish the Horde", it consumes 2 white mana.
2. There are 3 mana available to play in response "Guardian of the Faith", but the game dont let me play it, because "Vanquish the Horde" resolves instantly and dont let me respond with a spell that acts like an instant ( a creature with flash)