Mark 4:24
And he said unto them, Take heed what ye hear: with what measure ye mete, it shall be measured to you: and unto you that hear shall more be given. And he said unto them, Take heed what ye hear: with what measure ye mete, it shall be measured to you: and unto you that hear shall more be given.
The verse commands careful attention to what is heard, teaching that the knowledge received in response to Jesus' instruction matches the measure of sincere attention given to it. Taking heed means hearing for the sake of learning the truth so as to walk in it, examining closely and proving all things. It means believing not every spirit but trying the spirits whether they are of God, because many false prophets have gone out into the world.
Those who truly desire to understand will be satisfied, and their God-given privileges and light and knowledge will be increased with further light. Using those privileges will benefit them and, through them, others. Those who reject the light and reject truth will remain in darkness and lose even the little knowledge they have, falling into spiritual darkness and temptation.
Guarding what is heard and believed keeps a person from being found wholly deceived on Satan's ground. That guarding means giving no sympathy or support to those who hold fast to errors in the face of evidence and light, who condemn the church and those God has used to bear His message, and who speak with a strange voice, and instead hearing and following only the true Shepherd. The same care applies to reports about God's work and His servants, warning against giving them credence without care. People hear and report God's words according to the spirit in their hearts; those who are of God hear God's words, while others hear without understanding and remain unconverted and unhealed.
Hearing and understanding the truth brings blessing to the hearer and equips that person to benefit others through the use of those privileges. The light and truth received must be shared with others in words and work. Giving it out increases the capacity to receive and brings greater light and knowledge, and giving away heaven's light and gifts makes room for fresh grace and truth from God, while one who only receives and never gives loses the blessing and the capacity to receive.