Christian action is a form of prayer. Belief comes with the kinds of prayer that are manifest in action. Live the life of one for whom the Good News of Christ is the ultimate truth. Live the life that assumes that in the end all will be well, the life that is underlain by the fact that in Christ no catastrophe is ultimate, no evil is final, and no death is forever and in time you will absorb the facts of that Good News. Christ does not ask that of you.
Christian belief is like teaching.
Teach a subject and you will know it far better than you ever could, just studying that subject. Feed the hungry, love your enemy, house the homeless, care for the dying, visit the lonely and you will come to know with certainty. In such belief everyone is set free from all those sins from which you could not be freed by the law.