The following article is an excerpt from this book.

Since David prayed, “May my prayers be counted as incense before Thee” (Ps. 141:2, NASB), one thing we may conclude is that not all prayers are as incense.  Some in fact may be offensive to God.  Such are those prayers that are offered with wrong motives, which come from a heart with impure desires (Ja. 4:1-4).

Christ is the sweet aroma of our prayers.  If our prayers are not sweet before God it is because we have not allowed Christ to dwell in us and change us.  But if He is our reason for living, if He is loved by us and if we have let Him be Lord over us, to teach us and guide us and help us, and if we have let Him renew our mind, thus, if we have received from Him such precious graces of faith and love, etc., then our prayers will rise up to God as sweet incense.

As Spurgeon has pointed out in His book, The Power of Prayer in a Believers Life, just as incense has a special mix of spices formulated just right to make the incense fragrant, our prayers are made sweet only when there is a mixture of precious graces that God has put in us, such as faith, love, repentance and humility.  These are the sweet qualities of Christ.  They are as the sweet spices making up the incense of which God is well pleased with.

Spurgeon wrote, “The prayers of His saints are acceptable with Him …because they are the pleadings of His Son.  The saints are members of Christ’s body, and as they plead, Christ pleads in them.  The very strength of their pleading lies in this—that they urge His merits—and the Lord delights to be reminded of His Son’s excellencies.  It is a theme that His soul delights in.”

So we have seen that the sweetness of our prayers depends on how we abide in Christ.  The more we abide in Him, we could say, the sweeter our prayers will be to the Father.  But let me also say this: God understands our weaknesses, and that we aren’t always as pure as we would like to be.  And just because we have sinned doesn’t mean that He will never accept us. In fact, God is waiting to hear our prayers. He loves everything we say to Him when we come to Him in repentance. And He loves to hear us pray just because we are His Children. Yes, He loves to hear the voices of His children; and He loves the unique way we pray.

And you know what else?  I think prayers are especially sweet to God when several of us, his children, pray together in unity.  Each individual prayer has its own special flavor; but the prayers of a group of saints offered up together in unity I think brings to God an even greater pleasure.  Thus God delights in united prayer as one who would sit back and enjoy the sounds of a harmonious choir or of a full orchestra.  Thanks and praise be to God for His special delight in us!