True faith is full of self-denial. Faith keeps us low. Paul didn't want us to be mistaken - 'It is Christ that lives in me, so don't live in my own power. It is Christ that keeps the house. I mortifying my corruptions and vanquish my temptations, but I am a debtor to Christ
Just as a hen protects her brood and allows them to nestle under her wings, so the Lord will defend His people and let them hide away in Him. In this way let us shelter ourselves in our God and feel overflowing peace in knowing that He is guarding us. (Spurgeon on Ps 91:4)
Many may sit silently, refraining from discontented expressions, yet inwardly they are bursting with discontent. This shows a complicated disorder and great perversity in their hearts. And not withstanding their outward silence, God hears the fretful language of their souls.