Altar
The first altar mentioned in the Word was the one built by Noah after he came out of the ark, after being saved from the great flood. On that altar, he sacrificed clean animals to the Lord.
Mountains represent the Lord because of their height; we need to raise our thoughts above worldly things when "talking" with the Lord. An altar is a small artificial mountain. When it's used in worship, it can call to mind this raising of thought. The fire and smoke that rise from an altar are symbolically being sent to the Lord.
Most altars were made from unhewn stones. Stones represent truths. Unhewn stones - ones that have not been shaped by men - represent truths from the Word, truths that have not been adulterated.
The clean beasts to be sacrificed represent good things, charitable acts done because they are right. The clean birds represent thoughts about doctrine and actions, and about what is right. Presenting these things is an acknowledgment that we have them from the Lord, and a giving thanks to Him for them.
In the Israelitish Tabernacle, the altar of burnt offering represented the acknowledgment of good and the altar of incense that of truth. For this reason this larger altar, which was outside by the door, was made of brass which signifies natural good, while the altar of incense was made of gold, which signifies love to the Lord from whom comes truth.
John 13:4-17
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arose from supper, and laid aside his outer garments. He took a towel, and wrapped a towel around his waist.
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Then he poured water into the basin, and began to wash the disciples' feet, and to wipe them with the towel that was wrapped around him.
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Then he came to Simon Peter. He said to him, "Lord, do you wash my feet?"
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Jesus answered him, "You don't know what I am doing now, but you will understand later."
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Peter said to him, "You will never wash my feet!" Jesus answered him, "If I don't wash you, you have no part with me."
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Simon Peter said to him, "Lord, not my feet only, but also my hands and my head!"
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Jesus said to him, "Someone who has bathed only needs to have his feet washed, but is completely clean. You are clean, but not all of you."
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For he knew him who would betray him, therefore he said, "You are not all clean."
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So when he had washed their feet, put his outer garment back on, and sat down again, he said to them, "Do you know what I have done to you?
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You call me, 'Teacher' and 'Lord.' You say so correctly, for so I am.
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If I then, the Lord and the Teacher, have washed your feet, you also ought to wash one another's feet.
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For I have given you an example, that you also should do as I have done to you.
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Most certainly I tell you, a servant is not greater than his lord, neither one who is sent greater than he who sent him.
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If you know these things, blessed are you if you do them.
