So if God is in us, why the struggle?

Like I said in December, God is in me....so why is it so hard on days to retain that sense of His presence? That peace, that love. God does not change, so where does it go?
As Paul says in Romans 7:21 So I find this law at work: Although I want to do good, evil is right there with me. For in my inner being I delight in God’s law; but I see another law at work in me, waging war against the law of my mind and making me a prisoner of the law of sin at work within me.
I heard a good explanation recently...here is a picture of it

The aim is to live out of the heart, which became filled with the Spirit once I submitted to God and gave Him my heart. Now He has renewed my heart. My heart is now good, spirit-filled and influences my feelings, thoughts & will.

But feelings, mind and will are also open to whatever influences life throws at them - be it sickness or any kind of adverse circumstances. Then they start getting noisy....the feelings scream 'this hurts' - and I feel terrible pain. The mind then questions..'why does it hurt? Have I done something wrong? I can't handle this, I must be rubbish...why has this happened?' It wrongly concludes 'God cannot love me...' The will loses the will to fight, to draw close to God, or even the will to live! It is swamped...and of course the enemy adds his 2 cents worth of lies and accusations too.

I am not strong enough to excercise will-power to get me out of this hole.The aim of course is to retreat to my heart, where God's spirit dwells and allow myself to hear His voice...allow it to still my mind...to calm the inner storm.

I think it will take a life time of practice to get there. Just as I reach that inner place of peace and assurance, something rocks my boat, feelings take over and I capsize all over again. January has been like that really.

I am reminded of commandos practising their assault courses. Time and time again, they go around in circles. Time after time they fail to 'climb the wall' and fall at the same obstacle. Yet each circuit, they are getting imperceptably stronger....one day, they will sail over the wall...

Understanding what is going on helps, but the battle is still to be won. I am weak, which is fine by God. I don't think I'll ever be strong, but I do believe that one day, his Spirit (which is training me) will rise up within me & provide His inner strength to enable me to walk by the heart, in freedom.
Jesus battled this too. In Gethsemene, knowing what lay ahead, he fought the same fight, he wrestled with loneliness, betrayal, and the knowledge of the terrible ordeal ahead. He was in inner turmoil and anguish, but concluded 'not my will but yours be done..' His victory is our victory, as Paul concludes Who will free me from this life that is dominated by sin and death? Thank God! The answer is in Jesus Christ our Lord.

I am grateful the God's love is here for me, whether I am living by His Spirit or lost in my feelings. It is not a case of success or failure, more a growing experience of walking by His spirit with a heart that is free, full of peace and ready to love....one day ;-)
So I pick myself up & confess that one day I will say, with my God I can scale any wall.
Psalm 18:29