Meditation means to engage the mind in thinking of the form of the Lord, of the qualities of the Lord, of the activities of the Lord and of the service of the Lord. Meditation does not mean anything impersonal or void. According to Vedic literature, meditation is always on the form of Viṣṇu.
In the Nṛsiṁha Purāṇa there is a statement about meditation on the form of the Lord. It is said there: "Meditation focusing on the lotus feet of the Supreme Personality of Godhead has been accepted as transcendental and beyond the experience of material pain and pleasure. By such meditation even one who is grossly miscreant can be delivered from the sinful reactions of his life."
In the Viṣṇu-dharma there is a statement about meditation on the transcendental quality of the Lord. It is said, "Persons who are constantly engaged in Kṛṣṇa consciousness, and who remember the transcendental qualities of the Lord, become free from all reactions to sinful activities, and after being so cleansed they become fit to enter into the kingdom of God." In other words, no one can enter into the kingdom of God without being freed from all sinful reactions. Sinful reactions can be avoided simply by remembering the form, qualities, pastimes, etc., of the Lord.
In the Padma Purāṇa there is a statement about remembering the activities of the Lord: "A person who is always engaged in meditation on the sweet pastimes and wonderful activities of the Lord surely becomes freed from all material contamination."
Meditation on Executing Devotional Service In some of the Purāṇas the evidence is given that if someone is simply meditating on devotional activities, he has achieved the desired result and has seen face to face the Supreme Personality of Godhead. In this connection, there is a story in the Brahma-vaivarta Purāṇa that in the city of Pratiṣṭhānapura in South India there was once a brāhmaṇa who was not very well-to-do, but who was nevertheless satisfied in himself, thinking that because of his past misdeeds, and by the desire of Kṛṣṇa, he did not get sufficient money and opulence. So he was not at all sorry for his poor material position, and he used to live very peacefully. He was very openhearted, and sometimes he went to hear some lectures delivered by great realized souls. At one such meeting, while he was very faithfully hearing about Vaiṣṇava activities, he was informed that these activities can be performed even by meditation. In other words, if a person is unable to actually perform Vaiṣṇava activities physically, he can meditate upon the Vaiṣṇava activities and thereby acquire all of the same results. Because the brāhmaṇa was not very well-to-do financially, he decided that he would simply meditate on grand, royal devotional activities, and he began this business thusly.