In heaven, the most beautiful souls are those that have sinned the most and repented.  But they made use of their miseries like manure around the base of a tree.
Bl. Mary of Jesus Crucified (The Little Arab)

God is my heaven here below. I live with him. Even when I am walking, we speak together without being interrupted by anyone. If you would know him enough, you would love him. If you would stay with him for one hour, you would know heaven on earth. St. Teresa of Jesus of the Andes (Letter 40)

Yes. I have a heaven in my soul, because God is there, and God is heaven.
St. Teresa of Jesus of the Andes from her Letters

"My patrons in Heaven and my chosen favorites are those who have stolen it - like the Holy Innocents and the Good Thief. The great Saints have earned it by their works; as for me, I will imitate the thieves, I will have it by ruse, a ruse of Love which will open its gates to me and to poor sinners. The Holy Ghost encourages me, saying in the Book of Proverbs: O little one, come, learn subtilty of Me. (Prov. 1:4)"
~St. Thérèse of the Child Jesus and the Holy Face, from Counsels and Reminiscences

Lucho dear, throughout these days I have kept you here with me in this retreat... How I'd like to share with you what I feel, little brother of my soul. How I'd love to show you the lovely infinite horizon beyond creation that I experience and contemplate. I love God now a thousand times more than I did before, because I hadn't known Him. He reveals and makes Himself known to souls that really seek to know and love Him. Everything on earth, dear Lucho, seems to shrink, to lose value before the Divinity which, like an infinite Sun, continues to shine upon my miserable soul with its rays. Oh, if you could go to the depths of my soul even for an instant, you'd see me captivated by that Beauty, by that incomprehensible Goodness. How I'd love to bind the hearts of creatures and surrender them to divine Love! You've never known the heaven that I, through God's mercy, possess in my heart. Yes. I have a heaven in my soul, because God is there, and God is heaven.
St. Teresa of Jesus of the Andes from her letter to her brother Lucho

"It is not to remain in a golden ciborium that He comes down each day from Heaven, but to find another Heaven, the Heaven of our soul in which He takes delight."
~St. Thérèse of the Child Jesus and the Holy Face

When we consider the divine world that envelops us already here in our exile and in which we can move, oh, then things here below disappear;  all of that doesn’t exist, it is less than nothing.  The saints, for their part, understood true knowledge so well, the knowledge that makes us leave everything, and especially ourselves, so we can fly to God and live solely with Him!
Blessed Elizabeth of the Trinity from Letter 184

"In the presence of Jesus in the Holy Sacrament we ought to be like the Blessed in heaven before the Divine Essence."
~St. Teresa of Jesus

It does us much good to look into the soul of saints and then to follow them through faith right up to Heaven; there, they are all luminous with the light of God, whom they contemplate face to face for all eternity!… The Heaven of the saints is our homeland. It is the Father’s House where we are awaited, where we are loved, where one day we, too will be able to fly and rest in the bosom of Infinite Love!  
~Bl. Elizabeth of the Trinity, Letter 184

One day we went horseback riding with Teresa Lyon. You can't imagine a more beautiful landscape that the one we saw: huge waterfalls between two mountains covered with trees, and at the end of them, an opening through which one can see the ocean, above which clouds of different colors were reflected, and behind that, an overcast sun. You couldn't imagine anything more beautiful, because it makes me think of the God who created such a beautiful earth, even if it is a place of sorrow. What can Heaven be like - I often ask myself...
St. Teresa of Jesus of the Andes from her Letters

The proud person is like a grain of wheat thrown into water: it swells, it gets big. Expose that grain to the fire: it dries up, it burns. The humble soul is like a grain of wheat thrown into the earth: it descends, it hides itself, it disappears, it dies; but to revive in heaven.  
Bl Mary of Jesus Crucified "The Little Arab"