The former leader has died at the age of 55 and was found at his home in Fort William yesterday.
Tim Farron, a Christian, said: "I am utterly heartbroken about the news of Charles' passing. He was a colleague, friend and mentor. We've lost a giant today."
Charles, known as Charlie, Kennedy had been an MP for 32 years, but was ousted from his Ross, Skye and Lochaber constituency last month by the SNP.
The Lib Dem Christian Forum said the news was "desperately sad" and that Mr Kennedy was "always full of warmth & good humour".
Director Claire Mathys told Premier he was a man of faith: "He said he was a Catholic and he certainly did identify with the Christianity that has been a part of our British culture."
Christian Lib Dem MP Greg Mulholland told Premier it was tragic news.
He said: "He's had that natural touch and everyone he met really did warm to him.
"He had that natural friendly charm that I think made him a popular political figure as well as being a great political operator, which at his best he undoubtable was.
"He had that unique ability to really appeal to people, to connect and not seem like a politician.
"It's a huge loss to politics, as well as to the Liberal Democrats, but most of all to his family and friends and my thoughts and my prayers are with them on this very sad day."
Police were called to his home yesterday after being alerted by paramedics, but Premier understands his death is not suspicious.
Scotland's top Catholic, Archbishop Philip Tartaglia, said: "Charles Kennedy's death at the tragically premature age of 55 is a great loss not only to politics in our country but to the principles of civic and civilised engagement.
"His wisdom and courtesy were a mark of his highland upbringing, his political skill grew from his sharp intellect and his humility and concern for others was testament to his deeply held beliefs.
"He will be mourned by his family, by many in the world of politics and within the church, by the parishioners of St. John's Parish in Caol and beyond. Our thoughts and prayers are with them all at this time."
The Moderator of the Church of Scotland, Rt Revd Dr Angus Morrison, said: "He will undoubtedly be remembered as one of the most talented politicians of his generation.
"But he was much more than that. With his impish smile, distinct Highland voice and quick sense of humour, he was able to communicate effectively with people far beyond the circle of politics.
"His down-to-earth humanity ensured that he was held in affection by people of all political persuasions, and none.
"Raised a Roman Catholic in the strongly ecumenical community of Fort William, where his family is well known and loved, there is no doubt that this early experience continued to shape the political values which Charles expressed so well throughout his career.
"He will be remembered as one of the strongest voices opposing the UK's entry to the Iraq War.
"As a Church we wish to express our sincere sympathy to his former wife Sarah, to their son Donald, and to all in the wider family circle in this great loss.
"We assure them of our thoughts and prayers for God's presence and peace at this difficult time."
A statement released on behalf of his family said: "It is with great sadness, and an enormous sense of shock, that we announce the death of Charles Kennedy.
"Charles died at home in Fort William yesterday. He was 55. We are obviously devastated at the loss.
"Charles was a fine man, a talented politician, and a loving father to his young son. We ask therefore that the privacy of his family is respected in the coming days.
"There will be a post-mortem and we will issue a further statement when funeral arrangements are made."
In 2005 he admitted he had a problem with alcohol and resigned from the leadership of his party.
Christian Lib Dem MP Greg Mulholland speaking to Premier's Antony Bushfield:
Director of the Liberal Democrat Christian Forum Claire Mathys speaking to Premier's Antony Bushfield:
