St Isaiah the Solitary lived in asceticism at Scetis in Egypt and then in Palestine, dying in Gaza in about 491. He is mentioned in Sts Barsanuphius and John's book as a man of outstanding holiness (Answers: 240, 252, 311 etc.). He wrote much on the rebuttal of demonic provocations and on the need to be attentive to the conscience but few of his writings still exist, the majority having been destroyed. The Church commemorates the feast of St Isaiah the Solitary on July 3. 

Be at peace with your own soul
then heaven & earth will be at peace with you.

Enter eagerly into the treasure
house that is within you,

And you will see the things that are in heaven,
for there is but one single entry to them both.

The ladder that leads to the Kingdom
is hidden within your soul...

Dive into yourself and in your soul
and you will discover the stairs
by which to ascend. 

St Isaac of Syria (7th century)