The altar brings to mind, a place of sacrifice, something of significant value is given up.
Abraham gave up his son on an altar. Jacob sacrificed to God at an altar. Elijah sacrificed at altars, so dod Samuel and other priests and prophets.
Altars can be physical, mental or spiritual, like man's three dimensions. The most significant is the spiritual, for the unseen is not only the most powerful realm, the seen is also born from the unseen.
Powerful interactions take place at altars for better or for worse, determined by the parties involved. In scripture God's love is manifested through the demonstration of his power, in many sacrifices.
The willingness of man to yield to God allows the Spirit of God room in the area of life where the sacrifice is made. The Spirit of God gives life. God's life brings supernatural transformation! Romans 9:9-10
Prayer is the spiritual altar where man yields the will to God, or any issue that needs supernatural intervention. Hence the charge to pray and not to faint, to pray without ceasing. "O what needs we often forfeit, O what needless pain we bear, all because we do not carry everything to God in prayer."