Charles Spurgeon Commentary 1 John 5:13-15

"These things have I written unto you, that ye may know that ye have eternal life, [even] unto you that believe on the name of the Son of God. And this is the boldness which we have toward him, that, if we ask anything according to his will, he heareth us: and if we know that he heareth us whatsoever we ask, we know that we have the petitions which we have asked of him." — 1 John 5:13-15 (ASV)

These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God. And this is the confidence that we have in him, that, if we ask any thing according to his will, he heareth us: and if we know that he hear us, whatsoever we ask, we knew that we have the petitions that we desired of him.

A very wonderful thing is prayer, yet it is not every man's prayer that is heard, but he that has the life of God within him shall have his petitions granted because the Holy Spirit will move him to ask in accordance with the will of God.