Some things have to be experienced to be understood, having passed through the babies, children, teenagers phases with my own children, it has come as a real surprise to experience the same feelings, emotions and joys as I hold or interact with my grand-daughter Rebecca.
There is something about the look of innocence in her eyes as she looks at me, the joy when she smiles and even at the way she falls asleep as I or or my wife rock her in our arms and sing to her (good job she hasn't learned to know good from bad singing yet!). There is a trust there which is not about understanding or being in control but in simply not being able to do anything else except trust that we have her best interests at heart.
It seems to get harder as we get older, to trust, I mean, life has a habit of shaping us and in response we find it harder to trust so completely because we don't want someone else in charge of us. For many of us trusting in a God who often seems pretty remote to us is difficult, especially when that God says we should have faith like that of a little child (Matt 18:3), that is trust him completely. Pretty well impossible for most of us because we feel less secure letting God call the shots and prefer to do as we want with no restrictions.
How does trust work? Well in a simple way it works like this practically - I can't do something, I know someone who can, but to accept what that person can do for me I have to surrender some of my control/ independence and rely to some degree on that person. I have a friend who is a mountain walking / climbing expert, I (on a previous trip) refused to climb a mountain in Wales (Britain) as it looked too difficult for me and I felt I would not be in control in that environment. A few years later, same mountain, my friend persuaded me to trust him, surrender some of my independence and go with him up that mountain - I did and enjoyed it, reaching the top and going even further than I expected.
When Jesus died for us he did an extreme thing on our behalf, something we could not do for ourselves, restore what sin caused us to loose, our relationship with God. The problem for us is that we want to believe but on our terms, maintaining control. Trust me like a child trusts, Jesus tells us, and then you will become my disciples. Just as I would not do anything that would harm Rebecca, God tells us that he will not harm us but seeks our good (Matt 7:10). Learning to trust God as he deserves, in reality is the only way to really walk in faith and relationship with him. He loves us, we can trust him.