I love this song both for its beauty and meaning. It is one of my favourite chorale pieces to sing. It was written by Thomas Tallis, an English composer, during the reign of Edward VI. The words are taken from The Gospel of John 14:15-17
15If ye love me, keep my commandments.What a wonderful promise.
16And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever;
17Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.