Charles Spurgeon Commentary Matthew 6:5-7

"And when ye pray, ye shall not be as the hypocrites: for they love to stand and pray in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have received their reward. But thou, when thou prayest, enter into thine inner chamber, and having shut thy door, pray to thy Father who is in secret, and thy Father who seeth in secret shall recompense thee. And in praying use not vain repetitions, as the Gentiles do: for they think that they shall be heard for their much speaking." — Matthew 6:5-7 (ASV)

Verily I say unto you, They have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret and thy Father which seeth in secret shall reward thee openly. But when ye pray, use not vain repetitions, as the heathen do: for they think that they shall be heard for their much speaking.

They seem to attribute a sort of power to a certain form of words, as if it were a charm, and they repeat it over and over again.

Not only do the poor Muslims and heathens use vain repetitions, but the members of the Roman Catholic and other churches that I might name do the same thing.

Words to which they attach very slight meaning, and into which they put little or no heart, are repeated by them again and again, as if there could be some virtue in the words themselves. Let it not be so with you, beloved. Pray as long as you like in secret, but do not pray long with the idea that God will hear you simply because you are a long time at your devotions.