Christ is risen!
So God, who knows the heart, acknowledged them by giving them the Holy Spirit, just as He did to us, and made no distinction between us and them, purifying their hearts by faith. (Acts 15:8-9)
Orthodox scholar John McGuckin comments on the human heart as a spiritual organ rather than as a physical one:
A significant aspect of the biblical, and patristic doctrine, however, is that the heart is not alone in its seeking, or even taking the initiative; for God has elected the human heart as the preferred holy ground of the encounter. As with Christ, the Logos Incarnate, so now in the spiritual life of the disciple the heart is destined to become the new temple of an indwelling holy presence. The heart is not a part of the human creature in the biblical understanding, but connotes the whole creature understood as having a capacity for a higher life, and ultimately a capacity for God who has given his church the instinct for his presence. The heart, therefore, is the person understood as a creature under the eye of God, a mysterious and holy reality even though creaturely and limited. (STANDING IN GOD’S HOLY FIRE, p 58)
St Isaac of Nineveh offers two thoughts on the spirituality of the heart as the place where God’s law and Spirit dwell:
“One who has God’s laws in his heart will find the Lord within them.”
“But when the power of the Spirit enters and dwells in the intelligible powers of the pious soul, then instead of laws that are [written] in ink, the commands of the Spirit are fixed in the heart. Which the heart learns secretly from the Spirit (cf. Jeremiah 31: 33-34; 1 John 2:27) without having need of the help of sensible materials mediated by the senses.” (ON ASCETICAL LIFE, pp 82, 110)
You yourselves are our letter of recommendation, written on your hearts, to be known and read by all men; and you show that you are a letter from Christ delivered by us, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts. (2 Corinthians 3:2-3)
It is up to each of us to transfer the word of God from the biblical text and to write it on our hearts. Love for one another is not an idea to be entertained in the mind, but a word to be written on our hearts which we live in our daily lives, thoughts, behaviors.
But what does it say? The word is near you, on your lips and in your heart (that is, the word of faith which we preach); because, if you confess with your lips that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For man believes with his heart and so is justified, and he confesses with his lips and so is saved. (Romans 10:8-10)