He is honoured as a martyr because he died for the Church. He was offered his life if he would abandon episcopacy but he refused for this would have taken the Church of England away from being part of 'the one Holy Catholic and Apostolic Church’ and made Her into a sect.
So we venerate him for his sacrifice and see in it inspiration for us today.
In the words of Dr. Mandell Creighton, Bishop of London 1897-1901 and a noted ecclesiastical historian: ‘Had Charles been willing to abandon the Church and give up episcopacy, he might have saved his throne and his life. But on this point Charles stood firm: for this he died, and by dying saved it for the future.’
Immediately upon the Restoration of Church and King on 19th May, 1660, the Convocation of Canterbury and York, now being free to assemble and act, canonised King Charles and added his name to the Kalendar of Saints at the revision of The Prayer Book (see example on main SKCM page).
It came into use with the authority of Church and State in 1662 and since that time parish churches and chapels have been dedicated under the title of S.Charles (often as King Charles the Martyr).
His reign saw the beginning of a revival of the Religious Life in the Church of England and the first attempt at Community Life (after the Dissolution of the Monasteries under Henry VIII), which began at Little Gidding and was encouraged by S.Charles.
He oversaw many schemes for the Church: the restoration and adornment of churches and cathedrals, the founding and advancement of charities, the improvement of the liturgy and the re-introduction of the episcopacy in Scotland. His reign witnessed, albeit briefly, a Golden Age for Anglicanism especially in spiritual and devotional writing which is still much appreciated today.