It's a mat placed in front of a door. You wipe your feet on it. It doesn't expect anything of itself, but to serve.
The one who wipes their feet on the mat:
Jesus Christ is the doormat, and the door.
"Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me." (John 14:6)
"Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber. But he that entereth in by the door is the shepherd of the sheep. To him the porter openeth; and the sheep hear his voice: and he calleth his own sheep by name, and leadeth them out. And when he putteth forth his own sheep, he goeth before them, and the sheep follow him: for they know his voice. And a stranger will they not follow, but will flee from him: for they know not the voice of strangers. This parable spake Jesus unto them: but they understood not what things they were which he spake unto them. Then said Jesus unto them again, Verily, verily, I say unto you, I am the door of the sheep. All that ever came before me are thieves and robbers: but the sheep did not hear them. I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and find pasture. The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly. I am the good shepherd: the good shepherd giveth his life for the sheep. But he that is an hireling, and not the shepherd, whose own the sheep are not, seeth the wolf coming, and leaveth the sheep, and fleeth: and the wolf catcheth them, and scattereth the sheep. The hireling fleeth, because he is an hireling, and careth not for the sheep. I am the good shepherd, and know my sheep, and am known of mine. As the Father knoweth me, even so know I the Father: and I lay down my life for the sheep. And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd. Therefore doth my Father love me, because I lay down my life, that I might take it again. No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father." (John 10:1-18)
We all will, or have, stood before that Door. The doormat is the invitation. The doormat beckoned us to the Door. "No man can come to me, except the Father which hath sent me draw him: and I will raise him up at the last day." (John 6:44) And we have made a decision at that doormat, at that door: accept, or reject.
The doormat compares to the cleansing of sins. Christ illustrated that analogy in the cleansing of the disciples' feet. "He riseth from supper, and laid aside his garments; and took a towel, and girded himself. After that he poureth water into a bason, and began to wash the disciples' feet, and to wipe them with the towel wherewith he was girded. Then cometh he to Simon Peter: and Peter saith unto him, Lord, dost thou wash my feet? Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter. Peter saith unto him, Thou shalt never wash my feet. Jesus answered him, If I wash thee not, thou hast no part with me. Simon Peter saith unto him, Lord, not my feet only, but also my hands and my head. Jesus saith to him, He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean, but not all. For he knew who should betray him; therefore said he, Ye are not all clean. So after he had washed their feet, and had taken his garments, and was set down again, he said unto them, Know ye what I have done to you? Ye call me Master and Lord: and ye say well; for so I am. If I then, your Lord and Master, have washed your feet; ye also ought to wash one another's feet. For I have given you an example, that ye should do as I have done to you. Verily, verily, I say unto you, The servant is not greater than his lord; neither he that is sent greater than he that sent him. If ye know these things, happy are ye if ye do them." (John 13:4-17)
Let's get personal: where do I fit?
Those who have passed through the doorway must, in turn, be as doormats to those around them.
"And he sat down, and called the twelve, and saith unto them, If any man desire to be first, the same shall be last of all, and servant of all." (Mark 9:35)
"But so shall it not be among you: but whosoever will be great among you, shall be your minister: And whosoever of you will be the chiefest, shall be servant of all. For even the Son of man came not to be ministered unto, but to minister, and to give his life a ransom for many." (Mark 10:43-45)
"And he said to them all, If any man will come after me, let him deny himself, and take up his cross daily, and follow me. For whosoever will save his life shall lose it: but whosoever will lose his life for my sake, the same shall save it." (Luke 9:23-24; see also Matthew 16:24-25 and Mark 8:34-35)
Sometimes, we can be doormats just by being there as ministers (servants) of Jesus Christ.
Minister to those within our own sphere of influence. Everywhere we go, everyone around us, is our sphere of influence. Our homes, our workplaces, our schools, and our communities.
And through intercessory prayer, we can minister to the world.
Minister to all people, because of the love of Christ, and only in the love of Christ. "Bear ye one another's burdens, and so fulfil the law of Christ." (Galatians 6:2)