Mark 4:23-25:

If any man have ears to hear, let him hear.
And he said unto them, Take heed what ye hear: for with what measure ye mete, it shall be measured to you: and unto you that hear shall more be given.
For he that hath, to him shall be given: and he that hath not, from him shall be taken even that which he hath.

See also:

Objection: Faith Is a Gift from God, Not Something You Work Up Yourself