Why, When, Where do Catholic use incense?

Using incense goes back to the Old Testament. The Altar of Incense was in the Holy Place just before and separated from the Holy of Holies (Tabernacle). Incense was thought in Jewish antiquity to be made with 13 kinds of spices representing all of creation to be dedicated for Gods use (Josephus, Jewish 1st century historian).  Similar to Josephus, Philo, a first century philosopher said that incense represented water (cinnamon), earth (cloves), galbanum(air), frankincense (fire); basically represented the whole of the universe to be offered back to God for His will.
 
The inner sanctuary of the temple (Holy Place) where incense was, represented also the soul of Israel and man but the outer sanctuary represented the body where burnt offerings of animals were. Incense was the climax of the daily Temple service after everything else was complete. A priest was selected by lot once in his lifetime to offer incense (ie. Zachariah) and then he and other priests would go out and pray for the people. 
 
Incense was used for purification and sanctification of the Holy Place. It also represented the prayers of the people going up to God. Today prayer in our Catholic faith also represents purification and sanctification of our personal temple for God. Incense symbolizes our prayers up to God which also purifies and sanctifies us (Ps141:2). Incense is also made of Frankincense like that given to our High Priest, Jesus, at his birth which represents priestly duties… and our priestly vocation by Baptism to sacrifice self in love for God and neighbor. 
 
We are body and soul, our whole being worships God. Incense is part of the sense of smell and sight that is incorporated in worship, a sweet-smelling visible sign of something more. Incense is a sacramental used to nourish the faith of believers and venerate God’s Word and presence (CCC1154).  It is a visible sign of invisible grace. It points to God’s presence, our prayers and sacrifice (Rev 8:3-4) and relationship with God, to the need for holiness and respect for God at important times.
Catholics use incense at various times. Sometimes it is mandatory and other times ad libitum, Latin for “at pleasure”. The General Instruction on the Roman Missal (GIRM) identifies five occasions when incense may be used ad libitum during the celebration of Mass: the entrance procession, the incensation of the altar at the beginning of Mass, at the Gospel, at the preparation of the gifts, and during the elevations of the Eucharistic Prayer (GIRM, 276). Incense at the entrance is used to sanctify the church and people in preparation for the mass. The incensation of the altar is combined with the words spoken that our hearts and sacrifice are acceptable to God. During the two tables of the Lord where God feeds His people with His very presence in the liturgy of the Eucharist and liturgy of the Word, represents the holiness of God’s presence like the cloud of His presence on Mount Sinai and our need to recognize His majesty and mercy to come to us. At funerals incense reminds us of the prayers of loved ones for the deceased who have finished their pilgrimage on earth for their eternal destination and the purification and sanctification needed to enter Heaven. Incense is mandatory during exposition or benediction of the Blessed Sacrament, Holy Thursday, and Easter Vigil. This is almost like bringing out the china, it is a solemn event requiring extra attention to the importance of the moment.
 

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