A large Poplar tree gives shade to my family on hot sunny days. The tree's shade is actually the tree's shadow. Here we get an idea of what David meant when he said in Psalm 91:1 He that dwelleth in the secret place of the most High shall abide under the shadow of the Almighty.
To dwell in the secret place is to take a seat in the presence of God. While we are sitting there His shadow or shall we say His very presence (can't have a shadow without an object or person) becomes our refuge and fortress.
A fortress is a place that is protected against attack, it is a fortified place, a stronghold.
The Treasury of David says, "He who dwells in an impregnable fortress, naturally trusts in it, and shall not he who dwells in God feel himself well at ease and repose his soul in safety."
Can you say the Lord is your refuge and fortress? Do you trust him? In this age of the rise and grind, self -made millionaire and scientific advances in medicine and technology, the need to pray and trust God, seems obsolete. Yet, we are encouraged to take all things to God in prayer, trusting him to come to our aid to protect us from enemies or to supply our needs.
As noted in The Treasury of David, "We have trusted in God, let us trust him still. He has never failed us, why then should we suspect him? Pray for the grace to say, "In him will I trust."