Overall I thought the piece was very eerie and played well with the sense of dread. A very good atmosphere was created and I look forward to find out what happens to these crazy, meddling kids.

A few pro’s and con’s :

I feel it needs a description of the procession early on instead of ‘ they’.
Good imagery and nice use of the word ‘testament’
What did remain of the main structure? Descriptions would add a little depth here I feel.
‘Where the door used to be’ – perhaps another description? The doors lying on their hinges at the side or something. What size is the doorway? Does the immensity or narrowness of the doorway add to the feelings of the characters?

Repetition of the word ‘night’. Seems a tad stale.

‘Somewhere nearby’ – Ambiguity? Details again I think might add to the feel of the piece.

“I don’t know. Some kind of incantation.” He replied. – Grammar. Should be a comma after the end of the speech followed by a non-capital H.

‘Stopped short of the doorway’ – I think this sentence would have more impact if there was previous detail about it as stated above.

Is the leader the only one chanting? If so, then there’s a plural of ‘chant’ that needs to be singular.

The direction of the wind – Maybe have a character experience this change instead of the narrator describing it? If the wind is then coming from the ruins I feel it would be best to add a little bit of fear by showing the characters fear.

‘they thought they’ – repetition of they which jarrs a little.

What is an anti-sound? I think of something that devours sound. Black-hole style. Is that what the character was thinking?

They – Description would be stronger for the start of this passage. Anxious? Nervous? Did they body movement betray signs of fear?

Brand new? Would a church look brand new? Or would it look well kept? In good condition?

Struck him completely – what did that striking do? Did it cause shortness of breath? Did it hit him like a freight train? A falling rock? Insight would add to the horror fear.

Every sense of his being compelled him to turn and leave that place, his very soul screamed for him to flee, but still he walked on – destiny awaited. – Very good ending sentence.