It was necessary for Jesus to take on human nature so He could go through everything we do on earth — rejection, pain, sorrow, temptation. Though He was God in flesh, He endured the whole human experience not as God, but as a human, with all our frailties. That enables Him, our High Priest, to pray for us with tremendous sympathy: "For in that he himself hath suffered being tempted, he is able to succour [relieve, aid] them that are tempted" (Hebrews 2:18).
Consider a dear, struggling sister. She loves Jesus but she is feeling discouraged, cast down, rejected. She thinks, "I've been deeply hurt and I have no one to talk to who really understands." Sometimes she wonders if God can forgive her for having such weak faith and she is on the brink of giving up.
Satan stands beside her, accusingly saying, “Look at this one! She has virtually no faith. What kind of Christian is she, God?”
Jesus sees her hurt and feels her pain. He knows that her faith is weak, that she is on the verge of giving up, so He comes before the Father on her behalf and begins to intercede:
"Father, I know what she feels because I've been there. I was rejected by My own flesh and blood. I was mocked by the religious crowd. Soldiers spat on me and put thorns on My head. I even cried, 'Why hast thou forsaken Me?' I sympathize with this woman, Father, and I have washed away her sins. I know she still has a heart for Me."
This is where Jesus' prayers for us come in: "Father, I would that she be forgiven for her discouragement. I would that she be given a new supply of grace from on high. Let the Holy Spirit come upon her with a special renewing of encouragement and give her a spirit of peace and rest. She is Mine, Father, and Satan cannot have her!"
Suddenly, out of nowhere, the woman feels encouraged. Grace is given to her through the prayers of our High Priest. He is touched by the feelings of our infirmities and He acts in mercy.