The great work of prayer is to lift up the heart to God

To withdraw the heart from all created things which we see and feel here below, that we may converse with God in heaven: “Unto thee lift I up mine eyes, O thou that dwellest in the heavens” (Ps 123:1) and “Let us lift up our heart with our hands unto God in the heavens” (Lam 3:41). Prayer doth not consist in a multitude and clatter of words, but in the getting up of the heart to God, that we may behave ourselves as if we were alone with God, in the midst of glorious saints and angels.

There is a double advantage which we have by this getting the soul into heaven in prayer. It is a means to free us from distractions and doubts. To free us from distractions and other intercurrent thoughts. Until we get our hearts out of the world, as if we were dead and shut up to all present things, how easily is the heart carried away with the thoughts of earthly concernments! Until we can separate and purge our spirits, how do we interline our prayers with many ridiculous thoughts!

It is too usual for us to deal with God as an unskillful person that will gather a posy for his friend, and puts in as many or more stinking weeds than he doth choice flowers. The flesh interposeth, and our carnal hearts interline and interlace our prayers with vain thoughts and earthly distractions. When with our censer we come to offer incense to God, we mingle sulfur with our incense.

Therefore we should labour all that we can to get the heart above the world into the presence of God and company of the blessed, that we may deal with him as if we were by him in heaven, and were wholly swallowed up of his glory.

Though our bodies are on earth, yet our spirits should be with our Father in heaven. For want of practising this in prayer, these distractions increase upon us. So for doubts, when we look to things below, even the very manifestations of God to us upon earth, we have many discouragements, dangers without and difficulties within: till we get above the mists of the lower world, we can see nothing of clearness and comfort; but when we can get God and our hearts together, then we can see there is much in the fountain, though nothing in the stream; and though little on earth, yet we have a God in heaven.

—Thomas Manton
The Complete Works of Thomas Manton, 1:60–61.