"As a proof that you are children, God sent the Spirit of his Son into our hearts, crying out, "Abba, Father!" (Galatians 4:6)
As often as I am able to cry out from heart, "Abba, Father" I am reassured of the indwelling of the Holy Spirit in my heart. I should remember this each time I say the Lord's Prayer. Jesus Christ taught us to pray confidently to the Father. The Holy Spirit helps us to do so.