If there is a God then what we believe -- or not -- about Him, Her or It, is neither here nor there. Even less relevant is our sincerity. The same goes for science. All science is, is the naming and describing of what is there.
Witnessing is telling the story of how God came into your life. It must end with your accepting Christ, and then things are supposed to be all right with you. You're not supposed to be hopeless and want to die.
In my life, grace has emerged when I least expected it, as a sudden and thrilling validation that my heart's deepest hopes were heard and answered, sometimes even before they were formulated as thoughts.