"O for a Thousand Tongues to Sing" is a Christian hymn written by Charles Wesley. Charles Wesley wrote over 6,000 hymns, many of which were subsequently reprinted, frequently with alterations, in hymnals, particularly those of Methodist Churches.

Charles Wesley was suffering a bout of pleurisy in May, 1738, while he and his brother were studying under the Moravian scholar Peter Böhler in London. At the time, Wesley was plagued by extreme doubts about his faith. Taken to bed with the sickness on May 21 Wesley was attended by a group of Christians who offered him testimony and basic care, and he was deeply affected by this. He read from his Bible and found himself deeply affected by the words, and at peace with God. Shortly his strength began to return. He wrote of this experience in his journal and counted it as a renewal of his faith; when his brother John had a similar experience on the 24th, the two men met and sang a hymn Wesley had written in praise of his renewal.

One year from the experience, Wesley was taken with the urge to write another hymn, this one in commemoration of his renewal of faith. This hymn took the form of an 18-stanza poem, beginning with the opening lines 'Glory to God, and praise, and love,/Be ever, ever given' and was published in 1740 and entitled 'For the anniversary day of one's conversion'. The seventh verse, which begins, 'O for a thousand tongues to sing', and which now is invariably the first verse of a shorter hymn, recalls the words of Peter Böhler who said, 'Had I a thousand tongues I would praise Him with them all.' The hymn was placed first in John Wesley's A Collection of Hymns for the People Called Methodists published in 1780. It appeared first in every (Wesleyan) Methodist hymnal from that time until the publication of Hymns and Psalms in 1983.

--en.wikipedia.org

Wesley wrote this hymn to commemorate the first anniversary of his conversion to Christ. He notes in his Journal:

"Sunday, May 21, 1738. I waked in expectation of His coming. At nine my brother and some friends came and sang a hymn to the Holy Ghost. My comfort and hope were hereby increased. In about half an hour they went. I betook myself to prayer the substance as follows: O Jesus, thou hast said, I will come unto you; thou hast said, I will send the Comforter unto you. thou hast said, My Father and I will come unto you, and make our abode with you. Thou art my God, who casnt not lie. I wholly rely upon thy most true promise: accomplish it in thy time and manner.
…Still I felt a violent opposition and reluctance to believe, yet still the Spirit of God strove with my own and the evil spirit till by degrees he chased away the darkness of my unbelief. I found myself convinced, I knew not how or when, and immediately fell to intercession."

The stanza that begins O for a thousand tongues to sing is verse seven of Wesley’s original poem. This work first appeared in Hymns and Sacred Poems in 1740.

--hymntime.com