And Jesus answering said to them, Have faith in God. Mark 11:22 (AKJV)
When the Lord or His Word tells us to have faith it’s in the same manner as telling a man to be a man. That doesn’t mean he is not a man, so he should strive hard to become a man. It means he’s already a man, he should know it, act like it and stay lined up to that truth.
For the believer “have faith” means you already have it; therefore know it, act like it is so, continue in it. It means exercise faith and this we do by hearing the Word and speaking it consistently.
Have faith, believe, trust, rest; all these mean to act as who you are in Christ. Have faith is another way of saying “act on the Word and continue in that same direction. It means act like what God says is true.