Tim Keller on Being Filled with the Spirit and Experiencing the Father’s Love

When the Holy Spirit comes upon Jesus at his baptism, he hears a voice say, ‘This is my Son, in whom I am well pleased. You are my Son and I delight in you.’ In the same way, Romans 8:16 tells us that the Spirit bears witness to our hearts that we are children of God. Part of the mission of the Spirit is to tell you about God’s love for you, his delight in you, and fact that you are his child. These things you may know in your head, but the Holy Spirit makes them a fiery reality in your life. 
Thomas Goodwin, a seventeenth-century Puritan pastor, wrote that one he saw a father and son walking along the street. Suddenly the father swept the son up into his arms and hugged him and kissed him and told the boy he loved him – and then after a minute he put the boy back down. Was the little boy more a son in the father’s arms than he was down on the street? Objectively and legally there was no difference, but subjectively and experientially, there was all the difference in the world. In his father’s arms, the boy was experiencing his sonship. 
When the Holy Spirit comes down on you in fullness, you can sense your Father’s arms beneath you. It is an assurance of who you are. The Spirit enables you to say to yourself: ‘If someone as all-powerful as that loves me like this, delights in me, has gone to infinite lengths to save me, says he will never let me go, and is going to glorify me and make me perfect and take everything bad out of my life – if all of that is true – why am I worried about anything? At a minimum this means joy, and a lack of fear and self-consciousness. 
In Ephesians 5:18, Paul says, ‘Don’t be drunk with wine, but be filled with the Spirit.’ Remember the disciples on Pentecost. They went out and spoke the Gospel in public with such a wonderful lack of self-consciousness that some thought they had had too much to drink (Acts 2:13). But their boldness was unlike being drunk in the most important respect. Alcohol is a depressant – it deadens parts of the rational brain. The happiness you may feel when you are drunk comes because you are less aware of reality. The Spirit, however, gives you joyful fearlessness by making you more aware of reality. It assures you that you are a child of the only One whose opinion and power matters. He loves you to the stars and will never let you go.

(Tim Keller, Prayer: Experiencing Awe and Intimacy with God, pp.172-173)