Isaac the Syrian, also known as Isaac of Nineveh (ca-613-700), was a monk of the Church of the East, commonly known as "Nestorian".  He was born in the region of Qatar on the Persian Gulf.  That part of the Arabian Peninsula was heavily Christian prior to the advent of Islam.  Isaac spent years poring over the volumes in the monastery library and acquired a reputation for sanctity and ascetic expertise.  He came to the attention of the Catholicos, who consecrated him bishop of Nineveh in northern Mesopotamia.  However, Isaac, probably quite sensibly, resigned his see after only five months and retired to the remote monastery of Rabban Shabur where he lived as a hermit.  There he wrote the ascetic treatises upon which his reputation rests.  Although the Church of the East rejected the decrees of the Council of Chalcedon and adheres to a Christology at variance from that of Orthodoxy, Isaac's writings have become universally accepted by both Eastern and Western churches because they do not deal with such controversial Christological issues. 

Probably the best study of Isaac is The Spiritual World of Isaac the Syrian by Metropolitan Hilarion Alfeyev of the Russian Orthodox Church (Cistercian Publications, 2008).  Pp 163-174 deal with the role played by veneration of the cross in Isaac's ascetical regime.  Icons were not unknown by the Church of the East, but the cross occupied a much larger place in the piety of the faithful.  On Good Friday, hearing what Isaac has to say about the cross is especially appropriate.

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For true believers the sign of the cross is no small thing, for all symbols are understood to be contained within it.  But whenever they raise their eyes and gaze on it, it is as though they were contemplating the face of Christ, and accordingly they are filled with reverence for it:  the sight of it is precious and fearsome to them, and at the same time, beloved...And whenever we approach the cross, it is as though we are brought close to the body of Christ:  this it what it seems to us to be in our faith in him.  And by drawing near to him, and gazing towards him, straightway we travel in our intellects to heaven, mystically.  As though at some sight that cannot be seen or sensed, and out of honor for our Lord's humanity, our hidden vision is swallowed up through a certain contemplation of the mystery of faith...

For the cross is Christ's garment just as the humanity of Christ is the garment of the Divinity.  Thus the cross today serves as a type, awaiting the time when the true prototype will be revealed:  then those things will not be required any longer.  For the Divinity dwells inseparably in the Humanity, without any end, and for ever; in other words, boundlessly.  For this reason we look on the cross as the place belonging to the Shekhina [divine presence] of the Most High, the Lord's sanctuary, the ocean of the symbols of God's economy.