“Only believe” sounds like doing nothing and I sometimes wrestle with it. I was brought up to work hard and make things happen, so I have a native aversion to anything resembling passivity and idleness. But believing is hard work and is the only work we need to do.
Try believing the truths and precious promises in the scriptures when everything around you screams the opposite. Try believing you are healed when you have symptoms of terminal disease and have been “given” months to live. Try believing you are fruitful when the “experts” say your womb is dead. Try believing anyone loves you when you grew up in an atmosphere without love and were severely abused as a child. Try following the news and believe there is a God of Love. Believing is not child’s play.
God characteristically chose a seemingly passive thing as the way for us to express our God-like ability to create and make things happen. Believing God is the way to become like God, which is our destiny. “Only believe” sounds like folding your arms and doing nothing but it only makes everything possible with God, possible with you.
Before we were conceived and while we were in the womb, we were preserved without our knowledge, without our help. We have no capacity to keep our hearts beating for one second nor ability to grow one strand of hair without using something we did not create. Why not intentionally trust the One who created us for his own pleasure and holds our breaths?
Without our help, God created the universe, the planet and the environment we are trying desperately to “save”. He is capable of maintaining all creation by himself. He wants us to believe He can meet any need in His universe, by Himself. I think Jesus was saying to Martha, “I do not need you to work for me or make anything for me, I only need you to sit and open up yourself to me.” Only. Believing opens us up to God and that is all we need to do.