Isaiah 26:3 You will keep him in perfect peace, Whose mind is stayed on You, Because he trusts in You.
Faith is believing in the unseen. Just because we cannot see God does not mean we cannot see the affect He has on everything around us.
We have this wonderful peace and Joy God gives us through our believing in Him and our faith in Christ as our Saviour.
It is the believing and trusting which leaves us with the peace and joy because our minds are convinced in Christ; not just because we have faith but because He is faithful toward us!