The sight and smell of incense is one of the defining characteristics of liturgical worship in the Orthodox Church. Many view the use of incense and censers as something that existed in the Old Testament as a symbol and is now unnecessary, but the Bible is very clear that incense is an acceptable and beautiful tool to use in worship.
It goes without saying that incense played a very large role in Old Testament worship. The Lord commanded Moses to make an altar to burn incense on (Exodus 30:1) and gave specific instructions on how the incense was to be made and when it was to be offered.
In the book of Malachi, we see a prophecy concerning the continuation of the use of incense in worship that goes beyond Jewish prayers: "For from the rising of the sun, even to its goign down, My name shall be great among the Gentiles; in every place incense shall be offered to My name, and a pure offering; for My name shall be great among the nations" (Mal 1:11). This prophecy is fulfilled in the offering of incense by Christians, among whom the vast majority were Gentiles.
There are also examples in the New Testament regarding the use of incense. In the book of Revelation we read about the 24 priests who, "fell down before the Lamb, each having a harp, and golden bowls of incense, which are the prayers of the saints" (Rev. 8:3,4).
In addition, we see that the Magi bring frankincense as a gift to Christ at His birth. This symbolized His role as the great High Priest.
In general, incense has the benefit of being a source of contemplation for those who attend the service. Children may not understand the sermon or have the attention span necessary to benefit from all of the liturgical prayers, but can still be effected through the smelling and seeing of incense. For them as well as us, seeing and smelling incense immediately puts us in a spiritual mindset. Our prayers and souls rise up to God in the heavens as the incense rises to the ceiling of the church.
"Let my prayer be set before you as incense, the lifting up of my hands as the evening sacrifice" (Ps. 141:2).