The question is what is the significance of Joabs grasping the horns of the Alter...
The LORD is my rock, my fortress and my deliverer; my God is my rock, in whom I take refuge, my shield and the horn of my salvation, my stronghold.Psalm 18:2 (cf 2 Samuel 22:2)
This verse begins with "THE LORD is"...Thus it clearly reveals that "the horn" is the LORD GOD HIMSELF, our salvation, our strength and our STRONG - HOLD . The BRASS Alter of Sacrifice and the Sweet ALTAR of INCENSE each had 4 horns. The Brazen Alter, to which Joab clung for his life, had one horn at each of its four corners. These are the horns to which the animal sacrifices of Israel during Temple times were "tied" or bound. This is nothing more than a clear / shadow - picture of Christ our sacrifice, THE Sacrifice, being bound, not only by by rope and spike, but by the UNDYING LOVE of GOD for HIS CREATION, to the four points of the CROSS. Laying hold of, grasping or holding firmly the Horns of the alter, ( entering into the STRONG HOLD ) foreshadows we Christians laying hold of the CROSS. It implied REPENTING, HUMBLING yourself and ASKING for GODS mercy and Grace to manifest and SAVE you from whatever it was that was pursuing you, whether it were a physical enemy, a spiritual entity or a bout of guilty conscience. The implication is one seeking deliverance with all his strength, mind and heart. It implies FALLING ON THE ROCK AND BEING BROKEN.
Because man is sinful, fallen and unable to help or save himself, God in His MERCY promised a PLACE of REFUGE. A way of ESCAPE from JUDGEMENT, PUNISHMENT and DEATH. The Alter being in service during "Old Covenant" times was, of course, only a type and a shadow or things to come. It was in service UNDER THE TIME OF THE LAW and according to the Levitical Law, even breaking the 6th commandment, thou shall not murder or kill, might be covered by MERCY or GRACE under certain circumstances. EXODUS 21: 12-14 *He who strikes a man so that he dies shall surely be put to death. However, if he did not lie in wait, but God delivered him into his hand, then I will appoint for you a place where he may flee. But if a man acts with premeditation against his neighbor, to kill him by treachery, you shall take him from My altar, that he may die.* Joabs grasping the Horn of the Alter did not save his mortal life, as Solomon had him there slain. Scripture is so deep and there are so many levels of revelation hidden in it. Joab here in one sense is a symbol or representation of CHRIST who took hold of the cross ( not as a guilty man but rather as a willing sacrifice for all other men! ) He also in another light, can represent the people whom the Lord says will come to him in the end saying LORD LORD ,, didnt we do all these things in your name? and he will sadly say to them, go away from me, I never knew you. Try exchanging the first words of Psalm 23:22 "the LORD is my rock...' with the WORD , or JESUS... and see if that makes the verse seem even more relevant and clear. Jesus is... the HORN of my SALVATION... Then consider why Joab grasped the HORNS of the ALTER... Blessings..